With the benefit of youth and the trusty Raleigh Areana (little wheeled one) about a day or 2 to get 4-6 decent pedal revolutions in (its a massive grunt to get a racer stood up), that increased slowly until I had to stop counting and judged it by how much of the road I lived in, until I could do all the road.
Practice on an uphill, as said you gotta be able to flip it, know your going to flip it a few times but can still land on your feet. If you trying to learn clipped in you will need to go straight to using the back brake to check it in an emegrency flip situation, rekon it might be easier to forget the back brake thing and learn on flats, dragging the back brake is great once youve nailed it, but just another thing to try and learn if you cant already wheelie.
And its going to be loads harder when your older.
BUT once you have it you will never lose it, it came back real quick once i started cycling again.