Time-based free trials are fine for one-time purchases I think. It's basically the equivalent of a return window, without collecting money upfront. Where they

Time-based free trials are fine for one-time purchases I think. It's basically the equivalent of a return window, without collecting money upfront. Where they don't make sense is for subscriptions, because subscriptions are by definition something your users will be using for a long time, and it might take them a while to realize all of its value and get hooked. For this stuff a free tier that funnels customers to the paid tiers usually works best. You can play with limitations by restricting features, or usage, or anything else, but you probably shouldn't restrict them based on how much time has elapsed since they first signed up. Let them get hooked at their own pace.