I'd go for up to 90 minutes or so, but couldn't see the practicality of any longer (I'd move closer). 3 hours a day on the bike is a tall order to maintain 5 days a week. I guess if the commute involved a longish section of rural roads that would make a difference to me.
Realistically, my biggest hurdle would be wake up time. I generally prefer to get 8 hours of sleep - particularly in the Winter, and am not very good at waking up. My deepest sleep tends to occur in the hours before 6AM, so anything earlier than 5:30 or so would be really tough for me to sustain.