It basically comes down to how flexible you are from a scheduling and personality standpoint. Even during the peak of hurricane season the odds of week-long vacation being affected by a storm are probably less than 10 percent , but obviously not zero. If the uncertainty is going to drive you nuts maybe wait until winter (but then the odds of a Norte costing you a dive day or two are probably much higher than a hurricane affecting you in summer ).
FYI: Cozumel can go years without a hurricane , or it can have 3 or 4 in a matter of months. You only begin to have a better idea 7-10 days out if storm formation in the general area is likely —the forecast tracks usually only tighten up around 3 days out (maybe 5 if models are in good agreement ). Just remember , there are probably 50 million people in the US who have to worry about hurricane season every year from the North Carolina coast all the way to South Texas (and that doesn’t even count the occasional storm hitting points further north ). Of course it is probably worse to ride out a hurricane in a foreign country than the US, but even that isn’t cut and dry.