If you learn on an R22 I'll be surprised if you're ready for solo in less than 20 hours, and even in a Schweizer 300 or R44 it won't make that much difference.. Hovering a small helicopter is simply not like anything else you'll have done in a fixed-wing aircraft. Having a go at flying a helicopter in the air doesn't show you that.
As for the post solo exercises....
Ex 13 - Hovering sideways and backwards. Often done before first solo, but it'll be new to you
Ex 14 - Spot turns...interesting in windy conditions!
Ex 15 - Vortex Ring recovery. Do you know what it is? Not difficult, but will still take a bit of time, and still new.
Ex 16 - Engine-off landings - very different to PFLS in a plank.
Ex 17 - Advanced Autorotations - speeding up, slowing down, looking at ground covered, altering rotor RPM for same reason...a lot there.
Ex 18 - Forced landings - put last two exercises together and try to make...not just a field, but any flat area. If you have extra hours, getting better at it than the average PPL(H) is not such a bad idea!
Ex 19 - Steep turns - won't take you long
Ex 20 - Precision transitions. Usually combined with...
Ex 21 - Quick stops. Great fun low level manoeuvring, not difficult, but you won't have done anything like it!
Ex 22 - Navigation. You won't need much, but you will need to learn about cockpit management when you can barely take your hands off the controls. But a couple of hours or so should do it.
Ex 23 - Advanced takeoffs, landings, and transitions - used to be called Operating Out of Wind, and that's basically what it is...because helicopters can!
Ex 24 - Sloping ground - New for you, and quite difficult.
Ex 25 - Limited power...how to take off and land when you don't have the power to hover...again, new.
Ex 26 - Confined areas - how to do a recce and then get in to that hotel landing site between the trees or your friend's postage stamp sized garden.
Ex 27 - instrument flying - a bit harder than f/w as such an unstable platform, but if you have an IR, I can't see it being a problem for you.
But I hope you can see now that you won't be twiddling your thumbs for any part of that 39 hours! It's a fun course, and you'll learn lots; enjoy it.
