I also don't dink around riding outside, rarely coast and am always working, so I don't notice much of a difference. On the trainer I am really working. No long easy rides; I limit my time to 90-120' max, but do some intense intervals during that time. I can't imagine spending more than 2h on a trainer and see it as worthless. If I do longer stuff on the trainer I may do the following. 1h trainer + 30' run repeating 2-3 times and building intensity.
I look forward to riding on the trainer, because I can easily sit within the specific power range without distractions of stoplights, etc and the deviation from hills, etc. Also, I limit my time and total sessions so that I don't get mental burnout and therefore have much more productive trainer sessions: 2 sessions/week in the winter (3 if it really sucks outside), always keep 1 session/week during all weeks including summer.
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