In my experience, it's mostly at dusk. They do not seem to attack everyone equally, either. They like the taste of some people more than others.

Be very careful what you do on the beach after dark, you will find the little critters can get into many places........

Yes but they love me - apply repellant as they seem to come "home" with me and keep on biting! I also carry the pocket wipes for when the mosquitos come out.

Burt's Bees insect repellent worked great for me and the kids. Not so much for the hubby. They absolutely love him. He loves st john but always prepares himself ahead of time to come back looking like he has the measles. LOL. Bring calamine lotion and alcohol wipes for the bites just in case. It seems they enjoy damp cloudy days too. In my experience waterlemon was the worst on a very dreary cloudy day. They were in swarms and they get in every place imaginable. However it is a small price to pay to be in paradise. Just stay away from the beach at dusk/dark or on a rainy cloudy day and you will be fine.

We try to be off the beach by four or five to avoid the sand fleas.

I was across the street from the beach today around 4 pm and the no-seeums feasted on my ankles.
Deep Wood Off with 25% DEET works great.

They don't get everyone. My husband, dark skinned, is never bitten but I can go onto the beach around 4:40 with long pants and long sleeves, and socks and they still get to me. Vernita at Bolongo Bay has some great stuff (tree oil?) that helps, but I think that if the no-see'ums like you, you're just sunk.