The high season, known as Platinum season at MVC, runs from July through August at the two Costa del Sol resorts ( also a couple of other weeks at the Marbella resort). I doubt very much that Marriott makes many award weeks availible during that time, as these resorts book to capacity during platinum season and demand greatly exceeds supply for the timeshare folks let along people coming in via Marriott.com. So you're sitting pretty with May weeks. You're still gonna have very nice weather in May although the chance of some rain exists as the wet season falls off. But rain would not be a deal breaker here as there are so many things to do with your time.

Actually June and September have basically the same weather as peak season, just a few degrees cooler. These months are also in demand, though one might snag a week in this time window if you plan ahead & are mindful of when the various European school and bank holidays are. You'll have lots of daylight in May. Enhancing this effect is that Spain is GMT +1 hour despite the fact that Spain is about the same longitude as the UK. This makes for later sunsets and more time to do things ( & conversely darker mornings -- in five years of doing two visits a year, we have yet to see the sun when we leave for the airport the last morning). In the summer, it doesn't get dark until 10PM. It's no trouble for a guest to adapt to the later dining hours of Andalucía. We ourselves usually eat dinner after 9PM as we really get into the entire experience.

Have fun planning your journey. Feel free to PM if you have any questions along the way.

Barry