The duration in the paywall works like a rental time from the moment they start to watch.
For example, if you enter 1 hour as the duration it means the viewer has access for 1 hour from the minute they first watch. This continues to countdown if they continue to watch the stream or not. So if someone starts to watch for 5 minutes, leaves for 25 minutes, and comes back to watch again, their original 1 hour of access will have expired.