First Right of Refusal in Idaho...is stepmom excluded?

ex has kids 60% of time and Primary Cust. He wants to add First Right of Refusal to our decree for anything more than 4 hours. I am wondering if this pertains to work schedules and if I should be asked before the children are left with his wife. He works 3 months on nights and 3 months on days and rotates that sched. If I were to agree to add this, does that mean when he is working his nights that I have first right to have our children with me versus them staying at the home with stepmom? It will be for more than 4 hours. Any help on this topic would be great. I want to have all the facts and details before I agree or disagree. He is saying it is just for when we need a babysitter for the kids. Which I never need a sitter for over 4 hours unless its summer when they are with me and I am working.