We were on one nap by the time we started nursery, but had to go back to two whilst there cos J would only nap for 40 minutes otherwise. I'd say his ability to nap longer improved at around 15/16 months. He'd been at nursery 3 or 4 months by then. Actually, he's lsn, so he started napping better at nursery than at home at that time, cos nursery tired him out more! We rode a lot out with ebt and catch up naps on home days, but I also found that sticking to the routine (within half an hour) was really important too cos J also won't tack on much and it stopped us going too far off track. Obviously at nursery things were all over the place though....!