I feel free meditating I don't set an alarm but if I don't enough time I choose a 10 to 12 min meditation so I don't be obliged to stop at the middle of the meditation and to feel free and benefit from it.
No of course not if I do I will feel rushed and the meditation won’t to the job I wanted it to do.I let myself take as much time as it needs even if it late at night.
I'm trying to increase my meditation duration because I can only just last 15 minutes so far, so I use an alarm. If you want to just meditate until you don't feel like it anymore no alarm necessary
This differs from day to day but so far I’ve found using the app sounds to set that mood and keep me in that space has been useful. It also stops my busy brain thinking about time, as I know it will let me know when that time is up and then I can choose if I want to return to reality.