Lord semine's ride is probably the biggest one to watch, since those guys will bail after about 3 days if you take too long. When you see no time to lose pop up while trying to rest or fast travel, that's your clue something urgent is happening. Feuding farmers can actually fail if you do other stuff first, and escort missions tend to dissolve if you wander off too long.

Pretty much any quest with group travel or town defense needs quick attention, but the game's better about warnings than before. Most side stuff stays available until you start it, but once you're in, keep an eye on those hidden timers. Just pay attention when npcs start getting antsy about moving quickly, they're usually not kidding around about the urgency. Maybe worth noting that post-battle stuff can move on without you if you rest too long, so stay alert after big fights.