In the first picture I circled the "start" flag.
Scroll way over with the arrow I circled near the bottom right of the screen (or however else) until you get to the "end" flag I circled in the second picture.
Move the "end" flag to however far you want. Maybe you can right click it and manually enter in how many minutes away you want it. You can do this before or after you record...I think.
Hopefully that's the answer!