I have had the privelage for the last few seasons, to be able to coach a group of talented young ladies in the art of skiing. This season I had a consistant group of 4, ranging in age from 16 to 22 years old. All of them are former olympic caliber, nationally & internationally ranked athletes in another sport. The youngest had only 5 days total (about 18 hours) on skis when she came to me. We skied together for about 6 weeks. 3 to 5 hours a day 4 to 6 days a week. Within 2 weeks (about another 30 hours), I would say she was at this level description...
Advanced: Low Level 8: Very good parallel form, understands mechanics of the turn, very good upper and lower body separation, weights and un-weights skis, upper body faces down fall line, skis “cross” or “swing” under body, can make carved connected railroad tracks by keeping both skis on edge throughout the turn on all groomed trails in all conditions at high speed, has good athleticism and conditioning, is challenged by several off-piste disciplines, can ski off-piste at this level on the Hardest Blacks in slightly less than ideal conditions.
We didn't get to ski a lot of powder or bumps, but when we did she was making quick progress. Her basic technique on the grommed & with a little more mileage in easy bumps, would have her passing the PSIA LII skiing exam IMHO.
So yes given the right circumstances, attitude, natural ability & oppurtunity, I would say someone can reach the advanced stage of skiing in 50 hours. Not me by any means, I've skied about 15,000 to 20,000 hours & I still have a hard time with Open Parrallel!