When setting out a parenting time plan, the number of overnights needs to be considered because of the impact on child support, if minimizing child support is important to one parent, or maximizing child support is important. Moreover, setting out a specific parenting time schedule has the advantage of giving the non-custodial parent a parenting time plan that the court can enforce. There's nothing I hate to see more than that the NCP will have "parenting time as the parties may arrange and agree." It's certain to create arguments.
The State of Oregon has an online overnight calculator that is very easy to use and readily modifiable to fit parents' specific goals. Moreover, once a parent plugs in the alternate weekends, holidays and summer parenting time, the times may be adjusted to ensure that the NCP and the children are getting sufficient time together. The Oregon parenting time calculator is set up on a two-year basis since most parents alternate the major holidays.
Once this is done, you have two things: (a) The specific number of nights and percentage of time spent with each parent and (b) the percentage. Then the two-year calendar may be printed out on paper or in a PDF file. Each parent will have a two-year plan set out on a calendar so that there is no confusion about which parent is to have the children at any given time.
The best part? It's free. Find it here on the Internet.