Originally Posted by Richard Cranium

Your post doesn't indicate what "zone 2" means to you in terms of perceived exertion. If "zone 2" is supposed to be easy, then stopping a few minutes make no difference to any fitness benefits. If you are stopping because of discomfort or fatigue then you need to address the specific bio-feedback and correct your exercise session's metrics. (use shorter periods, change bike fit)

Typically, the largest percentage of aerobic benefits is realized in about 50 minutes of activity. Unless your base-building work is being conducted in unison with high intensity work, your extra-long sessions are worth even less.