I think the beauty of a retreat, especially in modern days, is that it 'forces' us to physically and mentally get away from all of that stuff in samsara that drags us down (e.g. mortgage, car repayments). Putting aside the spiritual benefits for a moment, I think there are instant psychological benefits - by focusing away from mundane aspects of life, stuff which brings us a lot of stress, we get to recharge our spiritual batteries. It's a time out, so to speak. So I like HN's suggestion about the one session a day. I think doing at least one session a day will very definitely bring you benefits, and is something you should try to aim for.