The short answer
Set the rule once, put it on a timer or a device setting rather than on your judgement, and make the end of the session a predictable event rather than a decision.
- Decide the rule when nobody is asking, and write it down.
- Use device timers and downtime settings so the device enforces it, not you. This removes most of the conflict.
- Give a warning before the end: five minutes, then one.
- End at a natural break, the end of an episode or a level, which is worth far more than the exact minute.
- Protect two times specifically: mealtimes and the hour before bed.
What will ruin it
Content matters more than duration, and so does whether it is watched alone. A worse problem than too much screen time is unsupervised access to social platforms and messaging at a young age.
Why it works
Most arguments about screens are really arguments about who decides. Moving the decision into a setting that was agreed in advance changes the conversation from a negotiation into a fact about the device.
This is general information, not medical advice, and it does not replace a GP, a pharmacist or NHS 111. Call 999 in an emergency. Full disclaimer.