My commute must be a little unusual in that it can take anything from 40 to 70 minutes or so during the day, but the public transport options are more direct in the middle of the night, so if I do choose to use that option, it will usually take around 35-40 minutes! These being door-to-door timings. I'd say the 70 minute option (which is usually the one involving the most walking) is probably the maximum time I'd want if switching modes. I think I'd find a long-distance journey on, say, one train for a couple of hours could possibly be more bearable once a routine was found.
I once did a commute involving a short walk, Thameslink and Tramlink which was remarkably reliable - in fact, at one point I spent a good couple of months only allowing a few minutes' arrival time leeway, which was so consistently sufficient that my employer didn't mind on the few occasions it didn't work. It must be my favourite of all my commutes - 1 hour door-to-door for about £25 a week, IIRC. I don't mind busy services so much if it's reliable and cheap, as there's always a tradeoff, often with popularity.