None of the iOS meditation timers on the App Store are worth bothering with.
iOS has got built in timer functionality in the stock iOS Clock app (Instructions for setting timers can be found here). However, the default timer sounds are unpleasant (aversion!) to hear when returning from meditation.
The best meditation timer app I have used on Android is the open source Bodhi Timer made by the Venerable Yuttadhammo. This Android app contains a number of free timer sounds in Vorbis format here.
These sounds can be converted for use with the built in timer functionality of the iOS Clock app.
Convert the Vorbis files to "m4r"
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