I’ve made only a couple three week trips. Mostly, I arrive on a Saturday and leave three Sundays later. Maybe, one day I’ll get out my passports and count how many days it totals. My shortest RT from San Francisco was 31 hours. My wife is still on her green card and she went back to Thailand for a couple years. I thought she would have issues getting through immigration when she got back, so I went over, so I could go through the checkpoint with her. They held her in the SFO immigration office for a couple hours, then fined her over $500, but let her back in. She’s studying for the citizenship test now.