To be honest, I thought too that it'd be very hard to commit to "so much exercising", when I began taking my health back in hands earlier this year. Even though I have lots of time compared to other people (I work part time and from home), I have a constant panic feeling about "not having enough time" - no idea where this is coming from, as it is totally irrational and I know it; maybe it's still a reminiscence from a little over 1 year ago, when I had to travel 3-4 hours everyday to go and come back from work, and when time was *really* an issue.
Anyway - What I did was trying to relativize and see things differently. I told myself, for instance, that if I was able to spend 5 hours in a row during whole evenings, until 1-2 am, in an online game, then surely I could find 2 hours to drive to the gym and squeeze cardio or weight-lifting in this. It was more a matter of finding a type of exercise I would like; this way, I'd feel like going for the pleasure, and this worked. So, alright, I gave up on some computer time, but I feel so much better now that I just couldn't care less about not playing games or whatever.
Plus I also suppose that "90 mins of exercise" doesn't necessarily mean "90 mins at the gym". If one spends 45 mins at the gym and then takes 2 walks of 20-25 mins with the dog, or walking/taking the bike to work instead of the car, etc etc, it's also exercising, right?