Hi Wannabslim,
I spent around fortnight on each step I think, moving up to SS+ with just over a stone left to go, then 2 weeks on each one thereafter. Even on 810 cals I lost 6 lbs in a week, so I think I may have moved to 1000 cals after just a week on 810 (from memory!). Then on 1000 cals I still lost about 3 lbs in a week and remained in ketosis somehow, despite introducing carbs (the weird thing is that when I was on SS I would get out of ketosis REALLY easily, for example by taking some medication for a bad back!).
I reached my goal weight (13 stone) whilst on 1200 cals. I'm now just under my goal weight. I was concerned that I would start to gain weight during the higher steps, but this was based on unhelpful tales from people who had done VLCDs and then not followed the maintenance steps. So far, I have to say I that have followed each step from SS up to 1200 cals TO THE LETTER!!! It works.
All the best with your journey,
Judders74