Pokemon-go – Why won’t Incense stop

To make use of Battery Saver, once turned on, simply turn your phone upside down, and the screen will darken to display a faint Pokemon Go logo. The game will still be on, and will still track your movements - you just won't see it. However, you will still get a notification or rumble if you approach a Pokestop or a Pokemon appears, so you can quickly pull the phone out of your pocket to interact!

source: http://www.ign.com/wikis/pokemon-go/Things_Pokemon_Go_Doesn%27t_Tell_You

I tried it and when I turned my phone to the correct position the map appeared again.

In case this is a bug and your game gets stuck in battery saver mode, you don't need to uninstall. You may just go to the running applications list and stop it. When you turn it back on it should be ok and you can just disable battery saving mode. more info on stopping an app: http://www.gottabemobile.com/2015/05/29/how-to-clear-apps-on-the-samsung-galaxy-s6/

I also believe your progress is saved in your account (in a server somewhere), so uninstalling the game will not delete your progress.

Incense always lasts 30 minutes. What might be throwing you off is the fact that it lasts 30 minutes of real time (regardless of whether or not you have the app open). So, if you activate the incense at 1:00, it will go away at 1:30. It's also possible that a server glitch or inaccurate time on your phone caused it to last shorter than expected.