I don't think you will have a problem. VB peak time is higher Apr - June and we have never had a problem booking in any of those months. In fact we booked an OVIR and a 2 bdrm for next week at 7 months.
Maybe things have changed, but since the peak turtle hatching season (big draw) is May through July, historically it's been tougher to get to prime space at Vero at those times (in other words, it's more than just a "Spring break" thing). I did get a 2BR there in August several years ago at 7 months, but did that ressie day by day (and the MS CMs I dealt with all said I was smart to do that).
The other thing to understand about Vero is that contrary to assumptions it IS impacted by WDW seasons. CRO uses Vero heavily as part of packages, booking people into it in front or in back of a WDW stay. When we were there in August '04, that was reflected in the fact the check-in desk was perpetually busy 24/7 (people checking in and out constantly). So if you are staying at Vero during a WDW high season, keep in mind that impacts the environment at the resort (less laid back than during slower times).