I would say about 3 or 4 weeks of 2-4 sessions a week. I went from 8.5 feet to just over 9 feet. I hit mostly my quads glutes and low back. I have not built up the courage for hamstrings yet. for quads (with legs straight) I can go up to 55miliamps up to 75 on glutes (in a sitting position) and upto 50mA on erectors (in a sitting position).
Hurts like hell… but it does work. The effects fade quickly if you stop using it for a few weeks.