I hope other MBers chime in on this, but we have been to CN in March, April, May, November & December. The interesting thing we found is that in the Spring we have not had issues with the sand fleas, but in November & December we did. I don't know if it is a seasonal thing because of November & December being wetter months than in the Spring or if it was just luck. So I hope other MBers will chime in and let us know what time of year they went and if they got bit up. Perhaps you won't have to worry about it in March.
I do know that if you stay away from the beach at dawn, dusk, & night you shouldn't have an issue. Also stay away after a rainfall.
Congrats on your wedding. You will have a wonderful time. CN is one of our favorite Couples resorts.
Juliann & Jeff
Jamaica Soon Come