To my knowledge nothing has a global timer. And only a few quests have an actual time limit. But there you usually get some kind of warning if you are taking too long.

The only thing that's frequently time sensitive are individual encounters after you spotted them. So let's say you see two groups fighting. If you then take a long rest, the conflict is resolved and one side is dead. But if you have a save literally 10 seconds before spotting the encounter you could reload that, have a long rest, then walk the few more steps and the two groups are still fighting.

And even non violent NPCs can be time sensitive after spotting them. So if you see a person standing around, just talk to them immediately.

The exact distance when an encounter is triggered can be hard to judge sometimes. So if you want to make sure not to "miss" anything, have a long rest just after a fight. Walk around a little bit to see if any post fight scenes trigger but if not, it's usually a good spot for a rest. Also helps with getting rid of some lingering spell or environmental effects m