Things apparently get much more difficult between Stage 1 and Stage 2, then again in Stage 3. So the best time to shave some of that time off would be to double-up on Stage 1. Unfortunately, you won't really know if you can take that work load until it's too late. Another bonus to this strategy is that you just have to pass, as Stage 1 modules won't impact your degree classification. (Additionally, the assessment strategy for TU100 only requires a 30% on the final TMA instead of 40% on an EMA like most modules.)
The programming environment used in TU100 (called Sense) is just a modified version of Scratch if you want to get a head start getting familiar with that, though it's not in any way difficult. I'm planning on making maths easier by just doing MU123 rather than MST124, since it doesn't really matter to the degree.
I've been struggling with deciding whether or not I want to shave a year off, or make it easy on myself. I've decided that it's not really about being easy for me, but I'm very aware of my study habits, and realise that trying 120 credits would result in burn-out. So six years for me. But I feel your pain.
I will say that I haven't seen anybody yet say that the OU over-estimates (well, not by much) how much time you need to be able to devote to study each week, although it's easier during Stage 1. So if you've got the 32+ hours a week and the determination and motivation, it may be right for you. Or it may not be. But I hope I've provided useful points.