I have heard of this before. I have worked in preschool for 13 years and have seen all kinds of custody agreements. Sometimes they change everyother week, every 2 weeks or most have the standard everyother weekend. My sister and her X have an agreement 4 days with her 3 days with him each week. Personally I had a joint custody with X getting children everyother weekend and 1 visit per week after school. There are many options.
If you are concerned about consistancy for your child, then definately talk to your lawyer regarding this.
Hope this helps. Good luck!
-------------------- to my ex - what goes around, comes around. you'll get yours...