As a way to quantify the amount he was watching and so he would understand this boundary we made Technology Tickets: 10 tickets, given every week on Monday, each ticket worth 30 minutes of screen time. We decided that 5 hours over the course of the week would be a good amount to still allow Eric to enjoy watching films which he loves, would fit into our family life, and would be within the recommended guidelines. Eric has autonomy over when to use them, and understands that he gets 10 which have to be swapped in.
When they are spent we hang them up on a hook in the kitchen. We don't take them away as a punishment or add any as a reward. We really enjoyed designing and making them together and Eric and I each have our favourite ones! So far they're working really well for us and have created a much better balance.