While many child custody schedules simply split the time up equally between both parents -- the kids spend every other week at a different parent's house, for instance -- it is sometimes important to think outside of the box and consider more creative ways to set up the schedule.
For instance, some parents use extended visits when the children are out of school during the summer months. These often last for two to six weeks.
Why would you want to do this? There are many potential reasons and every situation is unique, but one potential reason is if your ex has custody during the school year to keep the kids in the same school. They live with your ex every single week, giving them consistency in life and making it easier to play sports, spend time with friends and do everything else students in high school and middle school like to do. To keep you involved, you get to see them on the weekends.
Rather than fighting to have them live with you every other week, making their lives more chaotic and stressful, you may ask to have them for six weeks during the summer. They have plenty of free time and their schedules are wide open anyway, so it's easier for them to come live with you. This really allows you to invest time and energy in your kids, perhaps by taking them on a road trip, going camping or otherwise changing your own schedule to match theirs. When they need to return to school and their "real life" schedule, you can let them go live with your ex again without feeling like you don't get enough time with them.
This is just one example, but it helps show how creative ideas can sometimes be best for all involved. Make sure you know about all of your options when setting up a child custody schedule.