It definitely helps to look at solutions explained in detail, and probably has the best rate of return when tech company offers can differ in several hundred thousand dollars per year.

As far as hours of practice it really depends on if you grasp the concepts of types of questions. I got hired at a faang with 2 hard, 13 medium, and 20 easy questions done, but I'm for sure an outlier.

I also did these courses:

https://www.udemy.com/course/js-algorithms-and-data-structur...

https://www.udemy.com/course/coding-interview-bootcamp-algor...

Definitely leetcode helped with that. Not sure if I could directly attribute that to the extras I got from paying. I paid for access to more problems and less waiting to submit solutions, mostly. The solutions to the problems can essentially always be found in the comments.