Zyxel T-56 (and all other modems) - auto-reboot timer

I would like to have an option to set a specific time and interval to automatically re-boot the modem.
Example: every day at 02:00 or every monday at 02:00

This would help to keep the system running smoothly.

At the moment I have the problem, that over time the speed of my connection drops from 100Mb/s (1000mbit) to 10Mb/s (100mbit) after a re-boot the system is back at full speed. So a re-boot on a daily basis would help me (and probably other users as well).