Sounds like you're right on track. A time does include the E, and everything else between the time he wakes from a nap and the time you start wind down and the next nap. 1.5 hrs sounds about right, and you are correct in assuming he might be ready to lengthen if his naps are shorting (is this what you meant by going pear shaped?). Babies are all over the spectrum when it comes to how much A time they can handle at any given month of age. I think my dd got to 2 hrs around 6-7 months. If there's anything else we can help you with, please ask.