DD1 goes to daycare one day a week and when I check their sheet of activities for the day, it always says she's had at least an hour's sleep, and until we get home she's great, but once we get home she's tired, cranky, and always crashes out earlier than her regular bedtime (she even went to bed without a bottle the other night!).
I think she just gets so much done at daycare, and has so much fun, that she could sleep for three hours and still manage to wear herself out by the time I pick her up!