Why would the agent override the computer? The minimum connecting times are established for a reason! Most domestic United/United connections at SFO require only 40 minutes. However, there are some published exceptions requiring 50 minutes. And certain TED flights to/from LAS are listed amongst these exceptions. If you're arriving into SFO on UA1650 or UA1652 (the 605AM and 7AM departures from LAS) then the MCT is 50 minutes. There are other exceptions, but I didn't go through the entire list.