dhcp automatic restart
auto I want to restart dhcp service at 12 AM. every night?
12 am? :) pfSense has a "cron" package where you can schedule commands or scripts as cron jobs.
How should the command for cron be?
Starting/restarting the dhcpd service looks complicated, but killing it should be easy.
You could try adding dhcpd to the Service Watchdog package, killing dhcpd at midnight, and then letting the watchdog restart it. You could have a minute or two downtime for dhcpd.