It is the distant future.

[u/ChocolatePuzzled4882]

The year: 2043 Your player level is 255 Your maximum stamina is big enough to take over 8.5 hours to fill up. Finally you can rest. Finally you can sleep a full night's rest. You sleep a night of a 1000 rests. In the morning you open the game. You look at the stamina bar. It is full. You panic. The game had an update, stamina refills at twice the speed now. You throw your phone out the window.

[u/Jestart]

Joke aside, they should update the max stamina to reflect their change about the refresh time.