It used to be 90 days, but AFAIK it's now 7 days if you don't have a paid subscription (1 year if you do). Also there's a 10-app limit.
I discovered this recently as I wanted to install Kodi on my iPad. I'm not an iOS developer, and can't bring myself to pay an annual subscription just so I can install open source software on my own device.
Maybe I'm missing something but what do you mean? As far as I know you don't have any restriction. The only restriction is that you can't submit the result to the app store.