Allow more flexible timings
I find this one of the best break timer apps available, purely based on the functionality. There's one problem with it though, in my opinion. The selection of timings is very limited, and may not be suited for everyone. Especially for the short breaks, there should be an option to have the interval longer than 10 minutes.
Wouldn't it be better to allow users to enter their own timing manually (both for the intervals and the break time), rather than choosing from a list?
It's closer to what some other applications such as https://breaktimer.app/ are doing.