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I haven’t been able to find it in the app, but I use Seconds Pro to design my intervals. Strava will run in the background while you’re using the app. It’s also available for iOS.
My favorite timer app is "seconds pro" It's easily worth the $5. I've never found another one with all of its functionality and customizability. I use it for my time-boxing with Pomodoros, I use it for my running routine, I use it for my workout routines, It's fantastic.
here's the free version. You can't save any timers with it, because it's really just a preview so you can see the value in the paid version.
If you want free, I would recommend looking around at the interval timer apps. HIIT is the acronym for "high intensity interval training" and is another term you'll want to search for.
If you have android the Seconds Pro (https://play.google.com/store/apps/details?id=com.runloop.seconds) will do what you want - it will let you create any combination of timers, play different background music for each, give a verbal countdown and announce what the next timer is for etc. I use it for workouts and as a pomodoro timer.
The free version will do all this but not let you save the timer, so you would have to create it anew each time. However the pro version is only a few dollars/pounds and is well worth it.
I use Seconds. Here
You can customize for different workouts. For S&S I have a count down timer that goes:
(1) 1 min "Prep" (2) 5 min "Swings" (4) 1 min "Rest" (5) 10min "TGUs". 17 mins in total and easy to see where I am at a glance.
The screen doesn't turn off while the app is on, which is also handy.