The Stamina is responsible for your character breath and can directly influence on your EXP/LOOT that you receive. It decreases in real time while you are in battle, but the hours will not back while you are online, your character needs being offline. For each 3 hours offline, will be recovered 1 hour of stamina.
Between 54:00 and 56:00 there is a small EXP Bonus for VIP Account players.
Between 53:59 and 15:00, you will have a default EXP.
Between 14:59 and 00:01, you will have a EXP reduced by half.
Arriving at 00:00, you will not receive EXP/LOOT.
Remember, Stamina can influence only on EXP/LOOT that you receive.
It doesn't influence catch.