Sandflies are annoying (if they are there at all) early AM and early PM and only if there is no breeze.
If you choose to be away from the breeze and you are a magnet, they'll get cha!
I'm a magnet too. I wear long pants and socks.
I am always careful....sometimes too careful...but I don't come home with annoying bites.
Rarely does anyone sit on the sand. Use a lounge chair. Elevation away from the sandflies. (if they are there)
Mosquitos-prepare yourself as you would in any warm, damp climate. They live everywhere.
That said, let the this be the last thing to worry about. Go, enjoy and have a wonderful vacation.