PreE 2021 (Win) Timeline Marker questions

I'm struggling to make Timeline Markers useful to me.

Problem 1: after adding some timeline markers to flag places where I want to go back in and add titles, special effects, etc., I stretched a clip at the beginning of the timeline. NONE of the succeeding markers shifted by the amount of time I added. Is this how these are supposed to work? So, if I delete or add a clip, stretch a clip, whatever, all my previous timeline markers later in the timeline now point somewhere I don't want them to? This makes sense why? Luckily, sorta, PrE crashed while I was still trying to adjust all of these mangled markers so I lost all the bad locations. (And some effects I'd created that were part of the stretch and stuff that screwed them all up. Sigh.)

Question 2: There is a "Duration" showing in the Timeline Marker dialog box and the Adobe Help topics suggest this can be adjusted (what? nothing shows there besides the word "Duration"...) to create a marker that runs over multiple frames. Help also seems to hint that the right side of the marker will show duration/can be dragged to give the marker a duration. I'm finding no such capability/depiction. How do you create a Timeline Marker with a duration?