Recently I had to do late night restart of a Fortigate and was looking for "Reload in..." I found it, but in Fortigate it is a little different. It's called Daily Restart, and if you want to use it once you need to remember to remove this command later.
config system global set daily-restart enable set restart time 04:00 end
Now the FortiGate is configured to reboot at 4 AM (System Time).
Don't forget to update the system clock (Use NTP, Always keeps it synced)