It can be a good app idea.
Maybe.
I find the less I rely on my phone for organization the better.
Why? It's another step away from getting things done. It can crash. I can forget to use it. All sorts of reasons.
A big white board on the wall? Pretty robust in many ways.
I had a similar-ish system for when I was unemployed for a long stretch years ago. It was a white board I cut into 8 parts and labelled, "Exercise, Hygiene, etc..." Each contained 2 marks and each mark was a pomodoro 30 minute cycle. Very helpful.