Transmission is the default P2P torrent downloading application that comes with Ubuntu.
Starting and stopping on schedule
To run transmission from the crontab (/etc/crontab), it must be associated with a display as in the following example. The first line starts transmission at 2 am, and the second stops it at 8 am. Edit the crontab with sudo nano /etc/crontab, and add the following lines (replace username with your Linux username).
0 2 * * * username transmission --display=:0 0 8 * * * username killall -9 transmission
Now press CTRL + O and then hit return to save your changes to the file.
Quit option removed
The reason the --quit option has been removed is because the preferred method of running transmission in the background is as a daemon. See their wiki for more information.
Running on a server
transmission-daemon is a daemon-based Transmission session that can be controlled via RPC commands from transmission's web interface or transmission-remote. transmission-remote is a remote control utility for Transmission and transmission-daemon. By default, transmission-remote connects to the Transmission session at localhost:9091. Other sessions can be controlled by specifying a different host and/or port.