I have found over time nap changes do change with time ,how long they sleep for and when they go down.

I have always just got by what DD wants to do with day sleeps, if she shows me she is tired i put her in her sleeping bag and see if she will fall asleep( always on me ) then i will her down..if she sleeps for 10 mins or 1 hours or 3 hours thats up to her .

I trust her and that she knows how long she needs to sleep, if she wakes up and then is tired 5 mins later and wants sleep then she gets sleep.

Now that she is 6 months i dont let her go to sleep after 4, sometimes that cant be helped but i try to have the last nap of the day by then,she has her bath etc and is bed by 7-8 each night.If its been one of those days when she has had to have a later nap ,then she will be in bed later that night, it all deoends on how the day has panned out with sleeps .
normally its in bed 730, ,up for the mornng at 6-7 nap at about 9-930 then around lunch time then about 3ish

I say trust your baby,thry know when they need sleep, also growth spurts teething diff things will push them out of there normal habits for a while