Most of my past parents have always asked what I do here in regard to napping and they have followed that routine on weekends and days off. However, I have a new family and their son is 18 months as well. He is on roughly the same schedule as yours by the sounds of it. They pick him up around 4, have dinner around 430/5 and he is in bed around 530/6 and up at 6. Up until a month or so ago he was having 2 naps but they are now only doing one because that is what I do here. However, even with only nap he usually only naps an hour to 1.5 hours(usually always the hour or less tho) and than lays quietly in his playpen. He always poops an hour-ish into nap though and this is what wakes him up! It's so annoying lol. He's never tired or cranky though thank goodness. I think it's because he is getting such a long sleep at night!!

That is sad that Dad doesn't get to see his child in the evenings. Does he at least have a couple hours in the morning with her? I personally am not a morning person so this schedule wouldn't work for me but some people are morning people so maybe it's what they like?