My approved parenting plan clearly states: "In the event that either parent's residential time with the child requires a sitter for non-work related matters more than 3 hours, he/she shall first offer the other parent the opportunity to care for the child." My dilemma is this: The other parent is not employed & uses daycare for 1 hour in the morning before school and then 2 1/2 hours in the afternoon after school w/o giving me the opportunity to care for our son. This appears to exceed the set 3 hour limit or can this be interpreted as 3 hours consecutively instead of per day?

It does appear that way and sound like you have it on your side. Tell the people that wrote up the parenting plan that she is using daycare when she isn't even employed. Thing is that some day cares want the kids on a regular schedule and not sparatic drop offs so you have to make sure there is a back up plan when there is times you might not be able to watch your son. So check with the daycare if occasionally dropping a kid off is okay. If not come up with another back up plan before you talk to anybody about changing anything

I believe the interpretation would be "... 3 hours consecutively instead of per day". But it could go either way.