60/70 hours is, anecdotally, the ball park for someone coming to it "fresh". However, with a PPL(A), you will already have some airmanship, be familiar with a circuit (although helicopter circuits are lower and tighter!) and be happy with radio etc so it shouldn't take as long as someone who has done/has none of these.
However, I think 2-3 weeks full-time might be pushing it. I did my PPL(H) full time (as a fresher with no PPL(A)) and it took 8 weeks, flying Mon-Fri. That was 67 hours spread out over that time. I lost one day to weather but a few to serviceability of the aircraft. Other than that, I found 2 hours flying a day, as a learner, quite tiring. When I wasn’t flying I was doing my groundschool.
Cheers
Whirls