Redesign a popular fitness timer app

Physical Fitness

My app times my users' high intensity interval workouts (HIIT). It is a form of excercise where a short intense period is followed by a short rest period. These two periods repeat several times (called rounds). Users may optionally set a warmup and cooldown period as well. It can be used for many forms of excercise eg. sprints, jump rope, cycling, body weight excercises.

https://apps.apple.com/us/app/my-interval-timer/id1198752738

The app is live on the App Store using my developer design :) I do not have any strong preferences toward the design, I might lean toward flat or neumorphic dark designs that use a theme color similar to the existing one (FF9933).

My Interval Timer

The user lands on the Timer screen once the app has started launching. He can start a workout immediately using the presets by tapping the start/stop button (could be redesigned to use icons). An active workout can be reset using the Reset button. Tapping the gear icon leads the user to the Settings screen. He can edit timer, sound and other settings here. One of the buttons allow him to disable ads by way of in-app purchase (there is currently a banner on the bottom of the Timer screen and an interstitial ad when the workout is finished). Tapping customize sounds leads the user to our third screen, where he sees a list of sounds he can use to alert him that a round has ended. The user may tap and listen to any one of these, but can only change them after he has bought the in-app purchase for custom sounds. A CTA has to appear somewhere on the screen (currently is in the header of the list).

The app is iOS-only, therefore I would not like to see material design elements or solutions that would be foreign to most iOS users.

Every design category has flexible pricing for all budgets. App design starts at $599.