What works for me is that I only have a small glass of water or a coffee at my table. If I want to drink more, I have to get up and walk over to the kitchen. Early in the day this can be about about every 20-30 minutes, later it goes down to maybe 45-60 minutes. Then there are, of course, rest room breaks. So I'd say I get up and move 10-12 times a day in an unforced, natural way -- not always 8 minutes, mind, but it's about progress, not perfection.