I usually spend an hour, but sometimes I do it for more than two hours, probably because of my interest, so I think learning is quite interesting, whether it's math or something. I suggest you do some simple questions to cultivate your interest first. Doing it right will generally produce a sense of accomplishment and so on, thus increasing your confidence and interest, and then gradually deepening the difficulty. In terms of time, I think you should give consideration to other subjects, so you should allocate your time reasonably. I think it's better to spend an hour or so on this.