I ended up trying
Minimalist Pomodoro Timer - Goodtime Productivity for my Android phone. It worked very well.
Using the Pomodoro technique really helped with studies. The shorter stints made it easier to focus deeper during the stint, knowing the next break was less than 25 minutes away means I should make the most of this time.
The breaks were also a good reminder to stand and help my ergonomics and circulation.
The longer break after every 4 "pomodoros" were also a good time to maybe stop for lunch or a longer activity... I didn't always break for the 15 minutes as strictly recommended. Note, the app had this longer break disabled by default, but it was simple to activate it.
The regular breaks also kept pace and progress top of mind; prior to this I might "surface" after 2 - 3 hours only to that realise I didn't make the progress I intended.
Overall, the process helped with focus and pacing. Both things I wanted to improve in my studies.