Simply add/substract the in-point of the layer and possibly the comp start time in the main comp to the normal time property:
as always with expressions, I'm a bit baffled..
So the main comp is "main", obviously.
XYZ is the comp that holds the TC effect.
Does it matter how deep is the nesting ?
to which property in "Numbers" I assign the expression ?
I really appreciate this, I had about 20 different variations of this and couldn't get any to work. Thank you!
I'm not sure I understand what you're asking. If your main comp is called MainComp and one of the layers is a composition that contains the GUI elements and that comp is called GUI Comp, and you want to display the running time of the main comp then simply add a text layer to the Main Comp and add this expression to the Source Text property of the text layer. (to make this look good pick a monospaced font).
timeToNTSCTimecode(t = time + thisComp.displayStartTime, ntscDropFrame = true)
You'll find the code in the General category expression method menu avaailable in the timeline window by clicking on the little circle with an arrowhead icon next to the expressions.
To make the timecode read a different comp's timecode simply point to that composition by modifying the expression like this:
newTime = time - thisComp.layer("GUI Comp").inPoint timeToNTSCTimecode(t = newTime + thisComp.displayStartTime, ntscDropFrame = true)
If you have video that was shot with timecode then you can capture that timecode by selecting Use Media Source in the Time Display Style section of your project settings. You would then just put the name of the video layer where the GUI Comp is in the newTime = definition of the expression.
If your project isn't ntsc time code then delete the ntscDropFrame = true
That should do it.