[FEATURE REQUEST] Improve restart messages w/ UNIX timestamps

[ZenithVal]

Update messages should use UNIX timestamps instead of saying "in 15 minutes" See https://hammertime.cyou/
If using a unix timestamp in a channel that's not spoken in (so it won't be lost in chat) it would only need to be sent once, so an option to only send one warning in Discord would be nice.

A new message for "restart completed" would also be nice (Or editing the restart initiated message) for people to know when they can rejoin the server.

[egebilecen]

Hey, this is actually a good idea. I don't know why I didn't utilize this back then because I did use unix timestamps for !get_schedules command. I think I thought log showing X minutes ago text after the server restarted is ugly. Not sure. 😅