The issue with what constitutes the "first" weekend in a month is occasionally unclear. The OPTIMAL Calendar assigns the 1st/3rd/5th according to the common family-law definition of when the first weekend is.

As an example, we'll use April 2010. The 5th weekend of April 2010 starts on Friday the 30th. A Friday-to-Monday for this 5th weekend will cross the month boundary into the month of May. The Saturday and Sunday of that event actually take place on the first weekend in May, according to the calendar, and most parenting plans define it this way.

Because of this, the Calendar will assign the next event to the weekend of the 14th and 15th as shown in the image above, NOT the weekend of the 7th and 8th.

This is in keeping with the way that family courts generally interpret the calendar for assigning parenting time.