You shouldn't need to spend a lot of time on leetcode as a senior engineer. I do one leetcode problem every week from lists of recommend problems. You will realistically have 40 min of time to work on the problem, and you will go slower during the interview, so if I don't get an optimal solution in 30 min I give up and look at a solution. I'll spend at most another 30 min filling the gaps in my knowledge that will let me solve a similar problem next time I see one. I then add the problem to a queue of past problems I've failed. I've been doing this for years, but if you're just starting out you might need to cram more.

For side projects, I don't do them and have never had issues with that. I spend time reading stuff on my phone during downtime, which has been enough to keep me up to date on stuff.