I haven't connected through SFO (since it's one of my home airports!), but I can tell you that the International Terminal isn't connected to the domestic terminal; unless you want to leave the secured area, you'll have to take a shuttle between them. The UA map of SFO says that this shuttle departs "every 10 minutes during peak periods"--so, depending on whether they consider the time you're leaving a "peak period," I'm not sure how long it'll take! I'm sure it's a quick ride--the international terminal isn't more than a few hundred feet away from the United domestic terminal--but an hour might be cutting it close!