Not sleeping on time

18m old is having too much screen time every time he stays with his grandparents (once in 2 weeks) & doesn’t nap / go to bed at time .

Are these 2 inter connected?

P.s : I know screen time is a no no at this age but am working on that part with the grandparents.

So help me how to get him to sleep on time until the other one gets sorted if screen time & sleep are related ?

Thanks much .