Not knowing your travel dates, I cannot speak for actual times, but there seems to be a 7:00 or so flight each day, followed by an 8:30am or so flight.
Is the slightly later flight not an option for you because of a price issue, or do you need to be in SFO at a certain time?
As others have said, you are on the cusp of this itinerary being doable, if and only if you a) get in on time b) are an American Citizen, traveling under your US Passport and c) You are able to get processed through Customs quickly.
Even though, as others have indicated, this is a slow time for Customs, they will too have an abrieviated staffing level, so keep that in mind.
While I have not been present when you will be getting in, processing usually takes 30-60 minutes for US Citizens, and 60-120 for non-citizens. This is from the time the door opens, to the time you are exiting into International arrivals. I would think the low end would be accurate for your arrival time.
An important note for baggage. The baggage cut-off is :30 minutes before your flight's departure time, regardless if you are checking it at the counter or baggage recheck, so keep that in mind.