I watched the TV movie about Eisenhower starring Tom Sellick. They needed a full moon, calm weather and low tide. Moon and tide coincided once per month and weather was of course unpredictable. Severe storms had moved in on June 5 but they got a brief break in the weather landed on June 6.
In the movie they are discussing that if they dont go in June, the next window is July and if July is missed there may not be enough time to gain a foothold before winter. (I guess assuming an August invasion). Also the longer they had this huge army waiting around the more of a chance of the Germans figuring out their plans.
If there had been no break in the weather on June 6, and lets say its horrible weather again in July, what were the plans? Wait till 1945? A last ditch launch in August under bad conditions? It was also a morale issue with hundreds of thousands of soldiers confined to barracks waiting to go. They couldn’t have stretched that out another year. What was Plan B?