Office hours are a simple tool that will only allow emails to send in workflow during the time that you set. You let Dubsado know when your office hours are... say 9am - 5pm and it will only send workflow emails at that time. Any workflow emails there were to send during the off hours will be held until 9am the next morning.
It is simple to set up too! Head on over to TEMPLATES >> WORKFLOWS. Right on that workflows page you can find the set office hours text. Click that to set them! More about that here