When Share Play launches this fall on the PlayStation 4, you will be allotted a 60 minute long sessions in order to play or have someone else play your PlayStation 4 games. The news was first revealed by a French outlet and then later clarified by Sony.
Sony has confirmed with GameSpot that Share Play users will be limited to 60 minutes per session. There's no limit on the number of times you can use Share Play, meaning you can conceivably start Share Play up again and continue playing.

This essentially means that you can have hour long segments of time where you share your game library with an online friend, or they share their library with you. Once that 60 minute session is up, you can simply start a new one and continue playing. Though it does seem weird to even have a time limit in the first place if you can have an unlimited number of game sessions.