if I can share only one piece of advice with single parents who lament having to send their kids off to another house, it is this:
parenting time does not equal parenting influence.
be the very best parent you can be when your kids are with you. make good use of the time they are away to nurture yourself physically and emotionally.
you cannot control what is happening at their other house, but you can absolutely control the quality of attention and presence you share with them when they are with you.
don't get caught up in arguing with your ex over hours or days of parenting time. stay centered in what is important ... demonstrating your love and appreciation for your children, listening to them with your full attention, and living your own life as a model by behaving in ways you would be proud to see your children imitate.
love transcends time and space. keep that truth close to your heart.