These are all holiday related achievements. This includes ANY achievements that WERE RESTRICTED to holidays. Any deprecated achievements will be noted as well. Any broken achievements pertaining to specific events will be listed as well.

Some achievements that were holiday restricted that stopped updating were given updates to grant the achievements any time of the year are given honorable mentions in the unrestricted section.

This does not include achievements that were made and implemented for a holiday, but could be earned at any point of the year.

If you're aware of time restricted achievements that aren't listed here, feel free to comment. Need a confirmation that these achievements are indeed date restricted (at one point or another).

Feb 14th: [Company of Heroes 2] Romeo is Dead!
Feb 14th: [Coffin Dodgers] You Old Romantic
Mar 17th: [Batman: Arkham City GOTY] Storyteller

Apr 1st: [Batman: Arkham City GOTY] Storyteller
Easter: [Crimecraft Gangwars] Eggs Collector
Easter: [Crimecraft Gangwars] Eggs Cracker
Easter: [Crimecraft Gangwars] Eggs Looter
Easter: [Crimecraft Gangwars] Eggs Harvester
Easter: [Crimecraft Gangwars] Eggs Hunter
Easter: [Crimecraft Gangwars] Eggs Marauder
Easter: [Crimecraft Gangwars] Eggs Devourer
Easter: [Crimecraft Gangwars] Eggs Scavenger
Easter: [Lamia's Game Room] WHO_DO_YOU_THINK_YOU_ARE
Apr 29th: [Cave Story+] Happy Birthday Pixel!
May 10th: [Batman: Arkham City GOTY] Storyteller

Jun 19th [Dragon's Lair] Date with Daphne
Jun 21st [Batman: Arkham City GOTY] Storyteller
Jul 4th [Batman: Arkham City GOTY] Storyteller
Jul 4th [YOU DON'T KNOW JACK] Turncoat

Aug 16th [Batman: Arkham City GOTY] Storyteller
Sep 2nd [Star Conflict] Cosmonautics Day
Labor Day [Batman: Arkham City GOTY] Storyteller

Halloween [PAYDAY 2] First Nightmare
Halloween [PAYDAY 2] Second Nightmare
Halloween [PAYDAY 2] Third Nightmare
Halloween [PAYDAY 2] Fourth Nightmare
Halloween [PAYDAY 2] Fifth Nightmare
Halloween [PAYDAY 2] Pump-Action
Halloween [PAYDAY 2] Witch Doctor
Halloween [PAYDAY 2] It’s Alive! IT’S ALIVE!
Halloween [PAYDAY 2] No One Can Hear You Scream
Halloween [Terraria] Baleful Harvest
Halloween [Team Fortress 2] Masked Mann
Oct 29th [One Way To Die: Steam Edition] The Hallowest
Oct 31st [Batman: Arkham City GOTY] Storyteller
Oct 31st [Angry Video Game Nerd Adventures] Trick or Treat, Mothaf***a!
Oct 31st [Ostrich Island] Paparazzi
Oct 31st [Ostrich Island] Pumpkin Head
Oct 31st [Ostrich Island] Bonemian Rapsody
Oct 31st [Coffin Dodgers] Trick or Treat
Nov 8th [The Political Machine 2016] And the Winner Is...
Nov 26th [Batman: Arkham City GOTY] Storyteller

Dec 1st to Dec 31st: [Rush] Santa's Little Helper
Dec 1st to Dec 31st: [Toki Tori] Catch a Cold
Dec 15th to Jan 1st: [Left 4 Dead 2] Valve Gift Grab 2011 - L4D2
Dec 15th to Jan 1st: [Team Fortress 2] Valve Gift Grab 2011 - TF2
Christmas Event: [Champions Online] Winter Warrior
Christmas Event: [Champions Online] Broken Toy
Christmas Event: [Champions Online] Toymaker
Christmas Event: [Champions Online] Misfit
Christmas Event: [Champions Online] Winter Defender
Christmas Event: [Champions Online] Cold Iron
Christmas Event: [Champions Online] Northern Hero
Christmas Event: [Champions Online] Blizzard
Christmas Event: [Champions Online] Gift of Winter
Christmas Event: [EDGE] Snowblind
Christmas Event: [Interstellar Marines] Xmayhem Terminator
Christmas Event: [Interstellar Marines] Hasta La Vista, Baby!
Christmas Event: [Polynomial] Sore Throat
Christmas Event: [Serious Sam 3: BFE] Christmas in Cairo
Christmas Event: [Serious Sam 3: BFE] Reindeer Hunter
Christmas Event: [Terraria] Do You Want to Slay a Snowman?
Christmas Event: [Terraria] Ice Scream
Dec 19th to Dec 30th: [Revenge of the Titans] DRUNKEN FAMILY ARGUMENT
Dec 19th to Dec 30th: [Revenge of the Titans] SPROUT FLATULENCE
Dec 19th to Dec 30th: [Revenge of the Titans] NO-ONE LIKES XMAS PUDDING
Dec 19th to Dec 30th: [Revenge of the Titans] UNDERCOOKED TURKEY
Dec 19th to Dec 30th: [Revenge of the Titans] DISAPPOINTING PRESENTS
Dec 24th: [Shadows on the Vatican - Act 1: Greed] Ho ho ho!
Dec 24th to Dec 25th: [B.U.T.T.O.N.] Awkward Christmas
Dec 24th to Dec 26th: [Kill Fun Yeah] Tomteluva
Dec 25th: [Batman: Arkham City GOTY] Storyteller
Dec 25th: [Cave Story+] Merry Holiday Happy Euphemism
Dec 25th: [Coffin Dodgers] Christmas Truce?
Dec 25th: [Costume Quest] Tisn't the Season
Dec 25th: [Ostrich Island] Santa's Hat
Dec 25th: [Psychonauts] Christmas Shopping
Dec 31st: [Year Walk] New Year
Jan 1st: [Batman: Arkham City GOTY] Storyteller
Jan 21st: [Dungeon of the Endless] Endless Day
Jan 21st: [Endless Space] Endless Day
Jan 21st: [Endless Legend] Endless Day

Yes, this is the scum of all achievements. The list of games that have an early access achievement, or a preorder achievement and information regarding them. These are simply the currently ACTIVE ones. Ones with passed early access dates with no ways to unlock are moved to the deprecated section.

Dark Ages Rush or Early Adopter - By pre-ordering Age of Empires II: HD Edition or being an early adopter, you have demonstrated your superior strategic planning and advance preparation as hallmark qualities of a great leader. Now that your reputation is secure, give swift word to friends and allies to come and join you in the fight!

• "Pre-order achievement has been expanded to include early adopting so purchasing either expansion with in the first few weeks of launch grants the achievement." Source
  
• If you REDEEMED AoE II or any of its DLC within a month of its release, booting up the game and closing it will now grant you the achievement.

Early Bird - Play Damned Nation Reborn early access

• Currently in Early Access

Penguin Exclusive - Linux Early Access Adopter

• LINUX ONLY. Other builds MAY come later.
  
• Currently in Early Access

Notorious Commander - The player has taken the steps towards conquering galaxies in first wave. Early Access supporter.

• Currently in Early Access

Early access - Participate in Early Access

• Currently in Early Access

Community Helper - Help us create the game by playing in early access :)
Early Access Player - Play the game in early access.

• Currently in Early Access

Early Supporter - Because you're supporting us early and you're amazing

• Currently in Early Access

Any achievements that were previously time limited and had that restriction removed or any
achievements that were thought to be time related are listed here.

• Old One was previously a pre-order achievement. It can now be achieved by beating all maps on hard.

• Early Access achievements can still be obtained without any issues.

• All seasonal achievements (Summer/Halloween/Xmas) can now be obtained during anytime of the year via console commands.

• The 'Kickstarter Contributor' achievement now has a secondary unlock making it possible for anyone to unlock this achievement now. See this guide.

• The early access achievement 'Alpha Tester' can still be unlocked by completing the rest of the achievements.

These are the achievements that can only be obtained at a SPECIFIC DATE. This differs from the YEARLY DATES. (i.e.: Can only be done on August 12, 2001 or so)

The Original Release: Can only be done on August 25, 1985.

List of achievements that are NO LONGER possible to earn which were previously available for a period of time. List is alphabetically ordered.

• Valve Gift Grab 2011 – CS:S (Reason: Gift event no longer in game files.)

• I've Signed the DiRT Charter (Reason: no longer in early access)

• Special Services (Reason: no longer in early access)

• Charter Member & Beta 1 Tester (Reason: activation period over)

• Kickstarter Backer (Reason: no longer on kickstarter, trigger period over)

• Early Supporter (Reason: no longer in early access)
  
• Polygon Art Member (Reason: Dev-only achievement)

• Young Gun (Reason: no longer in early access)

• Citizen Army (Reason: no longer in early access)
  
• Waiting For The Recruitment Office To Open (Reason: no longer in early access)

I was there... - Played FortressCraft before it leaves Early Access!

• Developer is considering a change or removal of this achievement. (Nov 22 2015)
  
• Deprecated at this point.
  
• Source

Good Guy Nick - Plays games with free weekend players and helps them survive a campaign.

• Ever since L4D2 was offered for free on Dec 25th, 2013, Valve has not placed L4D2 on any free weekends.
  
• Deprecated at this point.

Kickstarted - Launched StarDrive on Steam. Test Achievement.

• It's currently in its Beta release, but it seems triggers stopped after April 2015. Not sure if the achievement has already been deprecated or there's no achievement user that has started the game for the first time after April.
  
• Also the Kickstarter isn't available. Currently destined for deprecated.

Just so if anyone who's been using this guide often, they can figure out what I've changed without having to look at everything again.

• Guide Completed
  
• [Survivor Squad Gauntlet] Added secondary achievement trigger for 'Alpha tester'

• [Mercenary Kings] Added secondary trigger for 'Kickstarter Contriubutor'
  
• [Pillars of Eternity] Added deprecation for 'Kickstarter Backer'
  
• [StarDrive Beta] Added monitoring for 'Kickstarted'

• [Terraria] Xmas and Halloween achievements added
  
• [Serious Sam 3: BFE] Xmas achievements added
  
• [One Way to Die: Steam Edition] Xmas achievements added
  
• [EDGE] Xmas achievement added
  
• [Polynomial] Xmas achievement added

• [Arclight Cascade] 'The Original Release' added to Exact Date

• Bridge Constructor added Easter and Xmas achievements