TL;DR The rule is, everything is almost always an ACTION.
What changes is how long that ACTION takes. In MOMENTS time, ACTIONS usually take only 1 ROUND. IN HOURS time, ACTIONS take 1 HOUR.
Supplementing what @Alex said, I always say that MOMENTS are the EXCEPTION, not the rule, even though MOMENTS come up more often in the game than any other time frame (mostly due to combat or combat-like intense encounters).
In the heat of combat or danger, adrenaline kicks in to keep you alive and your perception of time ‘slows down’. Someone can do an intense fighting for a couple of minutes and can swing their sword multiple times each minute but they can’t do it the whole day. It is simply not possible. Therefore MOMENTS cannot happen all the time. No matter how heroic and/or powerful they are, people still need rest (that’s what Alex is saying) between intense moments (hence MOMENTS, if you catch my drift).
Again, connecting this to what Alex said, if you frame MOMENTS like this then MOMENTS only happen when players are threatened / in peril / in danger. Otherwise they are back to MINUTES, 10 MINS, HOURS or whatever time frame that makes sense (your call as the GM).
In Alex’s example, Player 1 wants to recover, cast a spell and then loot the chests. Since there is no threat/danger, you say “Gentlemen, combat is over and we are in MINUTES time while you are catching your breath”. Recovery, casting a spell and looting the chest each take 1 MINUTE this way, instead of 1 ROUND.
Keep note that you could have said “Gentlemen, we are in 10 MINUTES time / HOURS time while you are catching your breath” instead. How do you determine this? It is your judgement call, depending on how much fight had already happened, how tired the characters are, where they are in the adventure etc.
Keeping the tension when being in HOURS doesn’t occur in my games because HOURS time means rest, exploration, hunting and similar stuff. If something exciting or dangerous is happening, I drop down to 10 MINUTES or MINUTES. Anything more exciting than this is usually combat and the like.
In addition to all this, sometimes I don’t even keep track of time. This usually happens when resting at night. Players say “I want to do this, I want to do that” and I go in order to keep the spotlight on them evenly and they do whatever they want to do, one by one.
Edit: My suggestion is, don’t let them split a given time frame. If they are in HOURS, they are in HOURS. Everything takes an HOUR, period. No more, no less. Looting a chest takes 1 HOUR, casting a spell takes 1 HOUR etc. You get the idea.