This is the fastest and the easiest way:

- In final composition ctrl+k and type your new duration (example: for 12 seconds, type 1200).
- Right click on layer #2 (composition name: 01) > time > time stretch, and add time stretch factor bigger than 100%. I just tried with 150%, it’s duration 12 seconds and 15 frames. Click OK.
For this example with 12sec, we just need to extend final composition a bit: ctrl+k and type 1215 (12sec and 15 frames).
That’s all.

Another way is to extend all compositions:
- final comp
- 01
- edit text here
- stripes and of
- and maybe more compositions if it’s required
But the 1st trick is much faster and easier, and no need to dig into the project and to modify almost everything.