Mindful Tracker has been made solely to time unguided meditation sessions and then save them as "Mindful Minutes" in the Apple Health App.
Set a timer for a specific amount of time, or if you dont know how long you will be meditating, start a stopwatch. At the end of the session your Mindful Minutes will be recorded.
If sound is turned on a gentle chime will play at the end whether your phone is locked or open.