How to know time duration of In and Out section (or time duration of any area in timeline)

That is a great question. I think Ann nailed it for you... temp in out points, note duration on paper, make cuts if needed ( to delete section to be replaced) and put new clip in that space.

This has plagued me a few times and with same problem... knowing the duration of specific range of stuff on timeline.

Added to that problem is the balancing act between aesthetics and time code... like, I'd want to choose stuff to put in there that looks nice, rather than simply match time codes.

Usually what I end up doing is use a stopwatch and get the rough time of the section I want to replace and then start choosing what I like to replace it ( same stop watch plus a second or so ). I stick the new thing on a level above the one to be replaced and use CTI to do the actual cuts and drag down the new piece snapping to the cti so nothing shifts.

It's a pain in butt and slow but it works, especially for the aesthetic quality... and nothing else shifts around and messes up all the other video and audio levels.

A plus for putting the clip above is you can delete the sound from that clip if you have that embedded from camera.

I'm not at my editing computer now, but try right click > speed and duration (or similar wording) as if you were going to do a time stretch.

It should tell you how long it is. Then cancel.

I've moved this from the Using the Community forum (which is the forum for issues using the forums) to the Premiere Pro forum so that proper help can be offered.