How do I run a command at a certain time of day (IRL)?

I have my server running inside a screen session. I can then use cron (or anything else, for that matter) to send commands to that screen session.

As an example, here's how i broadcast that i'm about to shut down the server. Adjust the command to your taste

/usr/bin/screen -p 0 -S ftb -X eval 'stuff "say SERVER SHUTTING DOWN. Saving map..."\\015'

• -p lets you select which window to attach to.
• -S lets you select a named session to attach to.
• -X is the command you want to send

look here for more info on the screen command if you need it

Hopefully that'll let you do what you need.

edit:foolishly, i assumed you were using linux...simply because i am.