When to pick up passengers from a US airport (SFO) from an international flight

There is unfortunately no "rule of thumb" as there are far too many variables that affect how long it takes someone to get from the seat on the plane to the curb outside. This is true of domestic flights as well as international, although there are more variables when arriving internationally. For example, consider these:

1. The size of the aircraft and where the passenger is seated on it, which affect how long it takes to exit the aircraft; this could take twenty minutes alone.
2. The time it takes to get from the gate to international arrivals processing. In most cases offloading is by air bridge, but for example at Dulles, you might board a "mobile lounge" to ride to the processing center, which will not depart until all passengers are off the plane. In that case it does not matter how soon you deplane—indeed, it may be to your benefit to exit last, as that makes you first to get off when you dock at the arrivals center.
3. The length of the line at immigration, which is affected by the number of flights arriving around the same time, the ability of CBP to fully staff the station, whether or not the passenger is a US citizen or eligible to use expedited lanes, and so on. This could be zero, or in extreme cases, two hours.
4. The time it takes to collect any checked luggage. I would say for most people, given items 1–3, this wait may well be zero; as many US airports are understaffed for baggage handling, however, this could mean another half hour or even more.
5. The time it takes for customs processing. Again, for most people this will be a short wait, but people with questionable items may need to wait for a more thorough inspection, to pay duty, and so on.
6. The time it takes upon exiting the international arrivals area to get to ground transportation access; this may take some time because of the size of the airport or because of the amount of luggage.

Under ideal circumstances (e.g. a US citizen with Global Entry with no checked bags who is physically fit and seated next to the exit and arrives before any other large aircraft, etc.) this whole process could take twenty or thirty minutes, but of course that is hardly typical.

Customs and Border Protection does provide an Airport Waiting Times website which lets you look up how long the average wait is and has been for immigration processing at different terminals at different times of the day on different days of the year. This is arguably the part of the process with the greatest variability from day to day, hour to hour, and the website is updated daily, so it is a good resources to check.

I regularly pick people up from SFO (arriving internationally, with luggage) via car, meeting them outside. My personal rule of thumb is to be there at least 30-45 min after the announced landing and then drive a couple of rounds. 1 hr after landing is not uncommon.

Arriving nationally without checked baggage can be as quick as 5-10min.

Historically this depended very much on both time of day and nationality of your friend. I fly many times to SFO and had everything between 10min and 1.5h waiting in line time for immigration depending on how many inbound flights just arrived.

However they recently installed the self serving kiosks, which seriously sped up the process. I would therefore assume 45min might be a good estimate from arrival at the gate to the parking lot.