HH has only 5 GVs and only 21 1BRs and 21 Studios. There are 76 dedicated 2BRs. The busiest months are June, July and August.
Depending on your dates, 2BRs will offer the best chance for success right at 7 months. Many have also been able to get 1BRs and Studios at 7 months during the summer, but they are definitely not as plentiful as 2BRs.
I tried to book for this past June or July at 7 months. I couldn't get anything - we were open to studio, 1 br, or 2 br. Nothing was available. It was very discouraging. We were hoping to try Hilton Head but are limited to school vacation travel.