Hi! Glad you are liking the game, the stress falls off from 100% to 0% in 24 hours, so it's about 15 minutes to drop 1%. The digivolution times are:
Fresh 8h InTraining 16h Rookie 24h Champion 48h Ultimate 72h Mega 96h Ultra 120h Armor 72h DNA 96h
All this data and many more is on the Discord, also there are a lot of other players to battle and interact.
You can ask for advice there!