Do you have a custody agreement? Is it outlined in that agreement? The agreement we have says something like every other Christmas break. That means visitation starts as soon as the kids get out of school on the last day and visitation ends the night before school starts again. If you have agreed on Christmas visits, you should have it added to your court custody agreement so that it's clear to both parties.
What did you mean by Long Distance? I don't really think it matters what the distance is, as long as there is an agreement in place and both parties agree. Also it's good to make it clear about payment for travel or if you will meet halfway or that type of situation. Then one parent isn't out some money or isn't hasseled by doing all of the travel part. That is if you mean Long Distance as the kids have to travel a long distance.
Does this help?