DD does 90 minutes each way.
7 minutes walk, 50 minutes train, 5 minutes walk, 15 minutes train, 5 minutes walk.
She's Y11 now and has done this length commute since Y1 of Primary. And will do a slightly longer one next year.
The main thing is how faffy the journey is and how much walking/waiting. She quite likes the 50 minutes on the train. Guaranteed a seat, heating, wifi and she can get a table seat and do a lot of homework, or she downloads films onto her iPad and just chills out for an hour.
What gets annoying are ones with lots of connections, or long waits between, or long walks if it's raining. She could cut 20 minutes off the journey doing a different route, but it's a much longer walk at the end.
On the upside, she's incredibly independent and good at organising travel - knows how to re-route journeys, deal with rail replacement buses, find her way round a gazillion apps. She also has a season ticket so just goes into London at weekends to see friends etc.
When we were looking at Y12 options, we set the limit at 2 hours each way maximum - and only if it was the place of her dreams. In the end it came in at 1 hour 40 mins. And location is very handy for things she wants to do after classes so worth it.