make stoprclone.sh
#!/bin/bash
sleep 180m
killall -9 rclone
exit
in your rclone upload script add this before you start rclone copy
exec /path/stoprclone.sh &
Check if you have killall command if not do
sudo apt-get install psmisc
p.s. I assume you are running it on linux, if you run it in windows just add it to task scheduler and limit 3h time there.