It seems there is no cron on Whatsminer I tried to search here even on Google I can't seem to find cron for Whatsminer except for Antminer.

So I guess your only option is to use a device that can automatically shut down and reboot the miner it might be a "programmable outlet timer" that looks like this below



But you will need an outlet timer that can support a high amp. Since Whatsminer m20s consumption is around 3360W you will need a 4100w outlet timer.