What do you need to do to earn crate keys

The chances are determined once you open/unbox. The cases don't have pre-existing loot that you unbox.

And no, the time of the unbox does not affect your chances.

The chances have not been officially confirmed by Valve.

For item drops, it boils down to 5 categories:

1. Weapons
   • Individual skins that drop are parts of certain Collections
     • A year ago-ish several of the original weapon collection skins were retired, meaning you cannot receive them as a drop from the item-drop system
     • Collections that you can currently receive item-drops from
       • The Train Collection
       • The Mirage Collection
       • The Safehouse Collection
       • The Italy Collection
       • The Lake Collection
       • The Dust II Collection
       • The Bank Collection
   • Weapons originating from Cases cannot be found as a drop
   • StatTrak weapons cannot be found as a drop
2. Cases & Capsules
   • There are always 3-5 cases in rotation in the item drop system
   • As new cases come in, old cases are phased out.
   • Some cases are for Operation pass-holders
     • For instance, the current operation is called Operation Breakout, with a case called Operation Breakout Case
     • This means that the Operation Breakout Case will drop for only for Operation Breakout pass holders
   • Older Operation drops are available to anyone, but this usually up to Valve's discretion
     • The previous Operation, Operation Phoenix, had it's own case specific for its own passholders, called the Operation Phoenix Case
     • The Operation Phoenix case used to be only for passholders, but can now be received as an item drop by anyone
   • Sticker Capsules can drop
   • Exclusive Sticker Capsules cannot drop. For example, the Katowice 2014 Challengers capsule (had to be bought in-game)
3. Missions
   • This was introduced in Operation Breakout
   • Missions WILL not drop for players without the Operation Breakout Pass
   • Completing a mission will give you a weapon drop from 3 specific collections:
     • The Baggage Collection
     • The Overpass Collection
     • The Cobblestone Collection
     • This means the above 3 colletion weapons CANNOT be found through regular item-drop system

4. Souvenir Packages

   • There are sometimes tournaments that come around that Valve designs Souvenir packages for. By linking your CS:GO account to a Twitch account or GOTV account, you can watch matches and have a chance to receive a Souvenir Package after a match ends
   • It doesn't matter if you've paid for a ton of skins for the game or never spent a cent on the game, you can get Souvenir packages regardless.

5. Graffiti

   • Valve released a new update to CS:GO. It include graffiti/spray as well as other fixes. Most of them are Paid Sprays.
     • However, you can still get a basic spray as an item drop.