So simple is best. for travel there may be checks that have story effects and maybe a condition. but for fighting in the heat of day normal people from outside osirion (NPC’s) make a Save when the escalation die is even yes that means every round when it is 6.
Npc’s from osiorion and PC’s make a save when the escalation die is 6 and if they are wearing light armor they make one on 5 and 6. and heavy armor they make one on 3 and 6
the saves are as follows hot temperatures. easy, blistering temperatures normal and deadly hard.
failed saves use a recovery if no recoveries available they daze you.
the dazed condition can be removed only after a long rest. (since you are out of recoveries i imagine you would want one anyways.