It can be difficult to get into HHI at the 7 months, period. To get into HHI during the peak season is extremely difficult. While the peak season does officially start Memorial Day weekend and goes through Labor Day weekend, the spring break months (Mar/Apr), as well as the holiday months (mid-Nov thru NYE) are nearly equally tough to snag at 7 months. You can always find posts where people were able to get those blocks of months last minute, but it's just not easy.
As others have said, however, the ability to get a 2BR is much more likely regardless of when you book as the majority of the resort consists of 2BRs. Getting a 2BR in early to mid-May is possible--booking one in late May at 7 months is unlikely. Someone mentioned you might have to waitlist a day or two and that is true.
June: not so much as the water temp is still fairly cool, relatively speaking, until late June
July: good to very good by late in the month
Aug: good
Sep: good
Oct: water temp is usually okay early in the month, but the days will get cooler as a general rule