In general, one 2-hour session is not the same as those 2 hours spread over the week. One reason is that you can't work at the same intensity for 2 hours as you would for 30 minutes. Long runs are great if you're training for something, but I would recommend trying to squeeze in a few extra cardio sessions throughout the week. You can get a good workout in 20-30 minutes, so the quantity of time isn't as important as the quality of the workout. High intensity interval training is a good example of a challenging workout that's done in a short period of time.
Hope that heps,