This issue should be fixed as of the December 1st update (build 22143 or newer). If you're still seeing this, please let us know so we can investigate further. Thanks!
We're currently investigating an issue where structured workout interval timers move faster when a device is operating at a low frame rate (<20FPS) e.g. a 2 minute interval block will complete in 1 minute. This can cause workouts to complete in less time than intended and you may not receive correct mileage or time duration for certain workouts.
We have a potential fix for this issue we're working on and hope to release it soon. Thank you for your patience!
If your device is running at less than 20FPS, it's likely either not supported, you have other apps/programs running at the same time that are slowing down Zwift's performance, or there could be a hardware problem with your device.
If you're 100% certain your device does meet minimum specs, you may want to close other apps running simultaneously or have your device checked for issues. You can also see a list of our minimum requirements on our website.
If your device does fall below minimum specs, you could also take this opportunity to upgrade! Most iOS devices support Zwift, as do most PC and Macs made in the last 3 years, and any Apple TV boxes that support app downloads.