Children in first grade who had spent more time in non-maternal care from 3 to 54 months had more conflict with teachers and showed lower levels of social skills than their peers who spent less time in child care according to teacher reports.
Source:
"Social Functioning in First Grade: Associations with Earlier Home and Child Care Predictors with Current Classroom Experiences"
NICHD, Early Child Care Research Network
Child Development Vol. 74, Number 6. November/December, 2003. Page(s)
(HT: FamilyFacts.org)

"more time", "less time"
I apparantly need to look this up because specificity would be helpful. 40 hours not good, but 20 hours O.K.?
My wife stayed(s) home with our kids! Her choice! And a darn good one if you ask me!