In my opinion and exprience: 13 months old still need two naps during the day, the first one usually 3 hours after he wakes up in the morning and the second one is about 3 hours after he wakes up from his first nap. Try not to disturb his schedule or strech it for too long, babies can't fall asleep if they are overtired. OR you can strech it to 4 hours after he wakes up in the morning to have one long nap and just go to bed early like before 8 pm, I still think it is better to switch to one nap when close to 18 months old.
It is hard when you are not the primary caregiver of the kid.
