It's pretty cool, it's a good idea to create the responsibility of fulfilling an agreed commitment... excellent!! I'm not an educator like our friend @cryotosensei but his opinion is a very good idea. That of only using a rule of 3. I totally agree.

If it's a child under 10 years old, all these rules will be too boring to remember regardless of whether you stop using the phone or not.

A rule of 3 is more precise and has more impact, and obviously it's much easier to remember, to keep in mind.