Do you track workouts on training peaks? I would consider shorter trainer rides with more intervals. Like 2-3 hours versus 5-6 but with IM pace/tempo/sweet spot for like 15-30 min your amount of work should be equel to riding steady outside with stops, downhills, etc...I did a few 4-5 hour outdoor rides but a lot of 2-3 hour indoor hard rides. Found I was more than prepared for the long outdoor rides, saved a lot of time, and no additional bike maintenance. Also, the training stress is the same or better than outdoors.