Summerstock orders are for 90 days minimum, unless that's changed. The entire Summerstock operation is only for four months (May-Sept) anyway, so you wouldn't be able to split that period. As for splitting T10 orders, I've never heard of it happening.
The question I have for you is if being gone for an extended period is an issue for you, what are you going to do if/when you're involuntarily recalled? If you're needed for a year, you're going to be gone for a year. I can guarantee it will happen at least once in your CGR career. Of the five times I've been recalled, three of them were involuntary. Of those three, I was away from home for two of them.