Basically, most world map events have a 'Did you do it?' flag. They activate when they are loaded in for the first time, and usually notified by an auto-save. If you then leave the area enough to load a different zone, go through a transition, or just plain go far enough away to unload them again, then that turns that flag into "nope, you didn't!", and the event goes to its default end state. Time passed has literally nothing to do with this, unfortunately.
Definitely this is how it works but I think there are some points/flags in the game that go back and check to see if you've done previous events regardless of whether or not you've activated them and then progresses the "plot" along accordingly. IIRC if you get far enough along in the plot without ever getting close to the "Trapped Lae'zel" encounter she'll free herself and all you'll come across is a broken trap. Similarly Halsin will trudge up after the Grove battle if you complete it without ever having entered his cell area.
