Make sure u b back within that 1.5 hrs sometimes its busy thru security.
You should be fine, I don't believe there are any restrictions in SFO for leaving, regardless of Covid tests. In fact, since you're flying in domestically, you'll likely have to go through customs / international security either way, so might as well enjoy the area. SFO is about 20-30 minutes from SF downtown, depending on traffic. There's some nice places for food near the airport though, but nothing much to see/explore.
Yes, no problem as long as your test is within the prior 3 days. Since you're likely checked through with a single airline, you won't even need to show proof, as that is checked by the airline, not at security. If you collect checked baggage, then they will check when you re-check that. Safe travels!
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