All times of year are popular for Grand Villas. There are a limited number of GVs. They usually go quickly during the 11 month window regardless of time of year being reserved. They are sometimes available later but don't presume you can ever get one unless you call early in the 11 month window. Even then, you should seriously consider calling day by day to reserve at the opening of the 11 month window, meaning, for example, if you want June 5 to June 10, call July 6 the year before to reserve June 5, call July 7 to reserve June 6, etc. and make those calls each day as soon as MS opens.