What is speed limit when children are not present?

I live in a town where the basic speed limit is 25-35 mph. On a 4 lane street the speed limit is 25 mph when children are present. What's the speed limit when no children are present? Is there a rule to this?|||if you were driving past a school when kids were coming and going, the speed limit is usually lower than it would be if you were driving by at 10pm. Call city hall to ask about specific locations, sure beats a ticket or worse!|||Whatever is posted just prior to the "When Children Are Present" sign.