A lot of times I go out to kill time while the torrent download is running but I always miss when the torrent download is finished.

Can you add an opting that lats Tixati Stop/Pause finished download?It will be great.

There's an option to 'Stop seeding when ratio exceeds X" in Transfers\General section.
If I correctly understand your wish, this should do what you need: after torrent is fully downloaded and seed ratio is greater than XX %, then torrent status becomes 'Seeding ratio exceeded' and practically it's now in stopped state