Scheduling live update twice a day at a specific time.

We have our management server checking for updates at 11PM daily. What I want to do is have this done two times a day, once at 6AM and once at 6PM. I see that I can schedule it where the default is every 4 hours, which I will go back to eventually, but for now, I want to do it two times a day at the listed times. I do not see a place where I can schedule the hours to download it, just how frequently.