For me, things clicked in place at the 12th hour (6th session), I was then able to fly somewhat consistently then, in a straight line, on very gentle waves (but with at least 8s period).
I have now 48 sessions under my belt. After the excitement of the early phases where I wanted only to foil, I am now only foiling when the conditions are good for it - and gentle enough to avoid breakage risks -, and not for SUPing. Which means for me about once a month where I live.
I'd say these are the milestones you will pass on the first 5/10 sessions:
- taking off (the first hour)
- managing the left/right balance
- managing to stop the foil from raising
- be able to gain height again if you lose altitude
But thing can take a LOT more time if you do not read advice, or do not use straps (or a way to have your feet in the proper place), have a bad gear (typically a foil too small for your weight and waves), and not go in gentle steady little waves.
Then, you will need lots of time on (and above) the water to progress in reading the underwater wave, turning, pumping, using turns to extend flight time... just like surfing.
My progression log is at:
www.seabreeze.com.au/forums/Stand-Up-Paddle/Foiling/SUP-foiling--my-first-steps- but I must say I stopped posting in it since it tended to degenerate in idiotic flame wars about straps and mast placement.