We did Glen Cove to Montauk last year (beginning of July). The second day is definitely longer. You also need to plan for the tides going through Plum Gut, which can give you a big boost or slow you to almost nothing. If the timing is right, you can get up at first light and easily make Shelter Island. Plan on motoring to make the tide. You'll probably have to keep moving, even if there is no wind.
Again, your schedule will depend on the tides, as well as the usual weather considerations.
Best to plan some options. Port Jeff is one option, then pick another one that let's you put in a long first day. And plan an alternate weekend in case you need to postpone due to weather.
From the other thread, what type of boat are you looking at having surveyed?
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