I don't much see the point of a longer window than 15-30 min, to be honest. There are very few times when I've had to evaluate a mobile app for more than 5-10 m

I don't much see the point of a longer window than 15-30 min, to be honest. There are very few times when I've had to evaluate a mobile app for more than 5-10 minutes to decide whether or not it was worth the price of admission. A 15-30 minute window is a good compromise to trials, since it weeds out the folks who were never going to pay for the app anyway and doesn't require any significant risk on the side of the developer. No need to spend resources on developing special trial versions, and little risk that people will try the app, get the value out of it, then immediately refund. (Games with limited time of play, short stories, that kind of thing.) Refunds post the window (but probably within some other window, like 30-90 days or so) should probably still be possible, but I'd be ok with those kinds of refunds requiring a higher barrier to entry – even if it is just filling out some forms. Plenty of apps I've paid for have gone the way of crappy updates you can't downgrade from, bringing bugs and what not along the way. I'd love to get a refund to those since I effectively can't use them anymore. It'd be an incentive for developers to not alienate current customers. Although, maybe paid upgrades would be a better solution to be honest.