One habit that saves airport trips is checking the first and last trains, not just the next train. Two Sunday examples I checked today show why:

Denver — RTD A Line, Union Station to Denver Airport Station. First departure from Union Station Track 1 was 3:00 AM and the last was 12:30 AM, in the America/Denver timezone, with trains every 15 minutes through the day. The board was also showing live predictions for the next trains, so a live time there is an agency prediction, not just the timetable.

Portland — TriMet MAX Red Line, Portland Int'l Airport MAX Station. First departure was 4:56 AM and the last was 11:27 PM, in the America/Los_Angeles timezone, and those times were scheduled only, with live data unavailable.

So the same mistake has opposite costs: in Denver you can usually rely on a late train, while in Portland a late flight that lands after about 11:00 PM leaves very little room before the last train. Check the last train before you book, not after you land. The pages I used are https://train-bus-schedule.org/us/co/denver/rtd/a/ and https://train-bus-schedule.org/us/or/portland/trimet/90/ — I operate train-bus-schedule.org. The agencies' own sites are https://www.rtd-denver.com/ and https://trimet.org/.