I'm with Mel. Set it in stone and negotiate changes as required. Want an extra weekend? Negotiate to give her a weekend swap before the fact. To do it on the run though will cause all kinds of trouble for poor Scorp.
Me: 31, W: 29 T: 4 M: 2 Kids: 3 (SS: 7, SD: 4, D: 3) Separated, still living together: Nov 2013 Separate bedrooms: Feb 2014 W working away; kids with me: Nov 2014