We started when kid was still in crib and wouldn't go in to get them in morning until the green light was on. Then once they were in a bed it was pretty easy, they already knew what to do.

Would be easy for you to introduce now and then slowly move back the get-up time.

One note: make sure you have only red lights on at night. Blue light is bad for sleep cycles.

Tried and failed at 18 months. WOrked at 24 months

we didn't do it until 2.5. She understood it and could follow the rule at that age. Didn't try it earlier though.

When did you introduce one? I'm thinking it's a little early for 18mo DS to understand it but wondering if it's worth introducing now (we already don't go in his room until 6am, so it would just add the visual element to what we're already doing).