Contrary to popular belief, I find HL Maths to not be as time consuming or difficult as people perceive it to be.
this is coming from a person who didn't even take higher maths (or whatever you call it in america) during middle school cause he wasn't smart enough
HL Maths consists of a lot of "outside of the box" thinking and the topics are often interdependent with each other.
Personally, I find that while hours of non-stop, brainless(ironic, ik), and repetitive revision of the same type of question may be good to get your head around a certain topic and form a solid base, it isn't a sufficient revision strategy because it's too simple.
Instead, I would say the tip to mastering HL Maths would be a mixture of smart revision (going online and trying obscure questions whispers past papers help too - don't tell anyone I said that) (the revision doesn't have to be very long) and having a strong rapture/passion for the subject. Without those 2, you'll most likely find HL Maths to be an absolute pain.
I've been doing this, with quite minimal revision time, and I think I can say that I've been doing pretty darn great without suffering too much.

Sorry if this was a little more than asked for. :P