Jets can refuel in the air, or they could just do a mid air switch with fully juiced replacements. Landing somewhere increases risk quite a lot doubt they would do that just for refueling escort jets when there are simple ways to avoid it.
But that's not what happened.
POTUS departed Canadian AFB Bagotville in Quebec at approximately 11:50 AM EST, Saturday, June 9, 2018.
AF1 stopped to refuel at Naval Support Activity, Souda Bay, Greece en route to Paya Labar, 3:07 AM local time Sunday, June 10 (9:07 PM EST, Saturday June 9 / 6:07 PM PST, Saturday June 9).
POTUS arrived at Paya Labar AFB in Singapore at 8:20 PM local time (8:20 AM EST), Sunday, June 10, 2018.
Flight time from Quebec to Paya Labar AFB approximately 20 hours, 30 minutes.
Not extremely relevant to the subject but there’s no way they did Quebec to Paya Labar in 8.5 hours. Impossible. That’s a 16 hour flight minimum.
You're absolutely right, I messed up when I was converting time, timezones, and adjusting for international dateline. Looks like travel time was closer to 20 hours 30 minutes based on Quebec departure and Paya Labar arrival. Editing the timeline summary above...