Hobby: an activity or interest pursued for pleasure or relaxation and not as a main occupation
Time is a finite resource. No one knows how much they will have. Some people disagree with the concept of spending or wasting time, especially if it is your time they are wasting.
I do not think a hobby is a waste of time, if it brings enjoyment. I do think it is important to spend time in ways that have value.
Recently, I read Early Retirement Extreme (here on Amazon or free at the library).
I particularly liked the idea of useful hobbies. Things you would not do if you did not enjoy them, but that you do for usefulness as well as enjoyment. The author has a number of ideas. I tend to favor activities without a set endpoint, but that always allow for more expansion, such as music.
Sometimes, though, it is satisfying to start and finish a project. That is why I knit.