You are asking about travelling non-rev on a buddy pass, that is different from the regular stand by discussion you will see on these boards. There are UA employees who post on this thread, maybe one of them can help you.
I will tell you that if you can check loads on the flights you want beforehand, you'll have a better day that you do want to get to the airport early so you have the chance for multiple flights, just in case and that (sorry) you're on the bottom of the standby list for a seat.