it truly takes time, I think Id estimate maybe the first 500k-600k of lavas as pretty inefficient, after about 750k you get the clicks down and it becomes second nature. Honestly the worst thing about lava runes youll learn is if you used F keys before lavas, you are gonna be soooooo scrambled when u go from lavas to PVM'ing with F Keys, because your muscle memory of lava rune f keys are just wacky.
Feel free to shoot me a message if u got questions tho.