Perfect for what is required!

I needed an app to set different training periods for HIIT, and this app does exactly that.
You can set multiple intervals of different duration, as well as name then. If you are using headphones you will get a notification of each interval, so you do not need to look at your phone constantly.

Please note that you can only set time-based intervals, nothing more.

CastorKrieg about Workouts+ HIIT Interval Timer, v3.1