It never ceases to amaze me how I can, in season, go out and ride for an hour and 45 minutes without blinking an eye about the time.

Get inside on the trainer and good luck getting past 30 minutes.
The good news about that though is the fact that you really don't need to go much longer than 30 minutes a pop a few times a week if you just want to "get a little" for a couple of months until the spring season starts.