I'd personally like to see a 2 hour window. That gives enough time to wait for the app to download, and to take some time to actually use it and figure out if

I'd personally like to see a 2 hour window. That gives enough time to wait for the app to download, and to take some time to actually use it and figure out if it actually does what you need it to do, and then return it if needed. You just can't make any sort of reasonable evaluation with only 15 minutes to do all that.