Configurable CRON schedule

[i20]

Hello !

First thing first thank you so much for this great script, it makes my life so much easier <3

I would like to submit a feature request to make the CRON schedule customizable via the envvars like most of the rest.
Actually the CRON schedule is autoset on a random time but in my case I need to be able to choose it explicitly to avoid any issues with other scheduled tasks I have.

Until now I have to sh into the docker container after each (re)creation to crontab -e what makes the container auto update a little bit tedious.

Any thoughts ?