In the past, the rotation was a pretty routine 2 months off, 6 months on for most positions. However, as the line has expanded there are more family needs, etc. among all crew including the higher ranks. Thus, there are an increasing number of schedule adjustments.
CMs who have been with the line for a long time can request and get schedule alterations--we know one who requested a 4 month contract in order to finish the contract and be on vacation when her sibling was getting married. Another requested a routine of 4 on, 2 off in order to have more family time.