Is it illegal to ring someones doorbell on sunday in utah?

It's not against the law exactly, but if you don't have an actual emergency, you could be charged with disturbing the peace. In some places, approaching a house at night comes with a presumption of wrongdoing, so you could legally be shot and killed if you don't make a LOT of noise to let the homeowner know you are coming ... and making that sort of noise at night is disturbing the peace.

In any event, if someone says no and tells you to leave and/or leave them alone, you're guilty of criminal trespassing if you don't go away and leave their property. Don't be offended if they open the door with a drawn gun, since doing what you describe in the middle of the night is one of the classic lead-ins to a home invasion robbery.