If you have an Infinibee (or higher) subscription, you can use a do-less goal for this. Set the limit to 3 videos per day. If you watch less than 3 videos, those will roll over unless you retro-ratchet it.
If you don’t have a subscription, you can try using a do-more goal. (Link to another discussion about how to do this). I think philip’s example might actually be for 5 episodes per day, not 5 episodes per week?