Batman fans have already discovered one date-related Easter egg within Arkham Knight.
Arkham City featured a Calendar Man-related achievement that required you to play the game on a specific day every month for a full year. Thankfully, this one is a little easier.
Read no further if you want to work it out for yourself.
There may be spoilers ahead...
There's a long way to go until Halloween (hopefully Arkham Knight on PC will be fixed by then). But players who change their console or PC clock to 31st October can skip ahead and see a couple of extra scenes.
These moments will only play out if you have completed the Most Wanted mission titled "Creature of the Night" and captured Man-Bat.
Rocksteady's hidden scenes see Man-Bat escape from captivity. Watch what happens in the video below: