I don't quite understand what you want to do, but here's some hints:
To adjust the duration of your comp, open the comp, choose Composition/Composition Settings and adjust the duration.
If your sub-comp is referenced elsewhere, you can duplicate it and make a shorter copy, thus preserving the original.
You can slide the pre-comp layer to access either end of the layer, in order to access the handles at the end.
You can adjust the speed/duration of the precomp within your main comp by selecting it's layer and choosing Layer/Time and using Time Stretch or Time Remapping.
Hi Andrew, thx for reply. Ya it is about the handles ... to reach/adjust them I have to slide the layer and then slide it back to original position when done. A function like the shortcut "n" but for layers would be great to just position the cursor and define the out or in point with another shortcut. By the way, is there an equivalent to "n" to set the beginning of the workarea ?
"b" defines the Beginning of the Work Area.
"i" and "o" move the Current Time Indicator to the in or out point of a layer, even if the point is outside the assigned workspace of the timeline.
If your pre-comp extends beyond the original composition length then you did not move all attributes to the new composition. If you've changed the length of the main comp and the pre-comp extends beyond the the main comp it doesn't effect rendering. If the layers in your precomp is shorter than the original comp and you want to trim the pre-comp to the length of the layers there's a script for that. I'll gladly point you to it or you could Google "trim pre-comp script" and you'll find it there.
but doubleclicking won't bring those in/out buttons rather than opening the source-comps comp window.
Alt+double-click brings up layer view.
Great thx for helping !