I think most of us have wrestled with such issues. If you find your agreement is flawed and need to change it at the 11th hour and/or you've had some kind of change that will impact the arrangement i.e. work hours, etc. Then yes, change it before it's formalized. Or ask for a 6 month trial - where you can see how it works with a formal day to review. If you don't have a hard date for the review - it may not happen. Be prepared for the other side to have revisions, etc too.
I personally think it's best for the kids if their schedule is the same no matter what. Even if it is more difficult for the parents. Consistency is king. So they knew that next week, next month, etc what bed they will wake up in and when.
I have some comments regarding the previous reply by 25MLC, Roist and others. I'll pick those up on my thread.
M:50 W:53 MR:20 D:21 S:17 S:11 BD-Sept 2015 Suspected PA Sept 2015-Confronted W & OM Dec 2015 Actually EA In house Sep:Jan/16-May 2016 W moved out:May 22 2016 OM-Intro Oct/17-On scene July/Aug 2017