Source: http://lifehacker.com/sworkit-pro-adds-custom-interval-lengths-a-workout-log-1501133024
iPhone/Android: We're big fans of Sworkit Pro
The big new feature here is that you can now change the interval length so you're no longer stuck with 30 second intervals. You can also customize the workout order so it's not completely random every time, which is nice if you find an order that really works for you. Finally, you also get a new workout log that shows what you've been doing, how many calories you've burned, and more.
Sworkit Pro (99¢) | Google Play
Sworkit Pro (99¢) | iTunes App Store