I've read Heikell's pilot and many other web sites about the Meltemi and they don't indicate the number or duration you all observe. I'm sure they happen but it must be bad luck you hit the periods they do. And it appears, in general, they don't blow 24 hours but peak in the afternoon and die after sunset. So if you need to, sail early. From what I read and see in photos, there's a few sailboats there. My suggestion is still to ask the base manager.
Greek climate - wind statistics for yacht charters and sailing vacations in Greece
Weather conditions in Naxos, Greece - Oceansource.net
Meltemi: May the force be with you...
The meltemi winds appear in May and sometimes last till October, but they peak during July and August. Though their exact behavior differs from year to year, they generally start at the end of May as light northerlies that last for 2 or 3 weeks, and after a period of relative calmness, reappear dynamically in July and August, when they exhibit their full strength and the most steady behavior. These two months they usually blow from the NW in Paros, usually at 4-7 Bft, but may on occasion become very strong going above 8 Bft, always accompanied with clear, dry weather
. After the end of August, the meltemi weakens again.
The meltemi on a daily basis
On a daily basis the meltemi starts in the morning, reaches its maximum at around 2 o’clock in the afternoon, when the temperature is at its highest, and usually dies out at sunset. (Which means that in the days with meltemi the beginners should make their first “steps” in the morning or –better yet- in the afternoon.) This behavior lasts for an average period of 2-4 days, followed by a pause of one or more days. This pattern “breaks” when the meltemi exceeds 7 Bft. Then it keeps blowing during the night, and it may last for a period of 10 continuous days!
The frequency of the meltemi periods during the two months of July and August, varies from year to year. Some –rare- years they almost disappear, and in others there are 7 or 8 of them. In general, the weather
statistics of the last 15 years show that in Paros the meltemi reaches or exceeds 4 Bft most of the days (around 75%) of these two months.