In high conflict joint custody situations, the less you need to negotiate with your ex, the better. So do your best to honor the parenting time schedule exactly as it was outlined in your written agreement.
If something comes up that requires you to be away from home during your parenting time, don’t try to negotiate a change in the parenting schedule. Instead ask a family member or friend to care for your child, or hire a beloved babysitter.
You can avoid a lot of stress and conflict by refraining from asking your ex to be flexible in order to accommodate your needs.