Georgs.
The trip is do-able in that time frame and I did almost the same route, but from Lake Erie to the Keys and Bahamas 20 years ago on Spirit, a Jeanneau 23 sailboat.
However, I think that you would better off running longer each day, especially to get through the Erie Canal, I assume you are picking it up south of Lake Ontario. I didn't leave the Chesapeake until late October and ran into some very cold weather, although a C-Dory gives you much better protection than the cockpit of a sailboat.
Once I was on the ICW, I got into a cruising rhythm. Most people heading south, both power and sail, raise the hook not too long after sunrise and stop well before sunset. I would go through the charts and guide books and pick an anchorage or marina (I usually anchored out) the night before and would plan on stopping well before nightfall, typically I would be at anchor by 3:00 PM.
I ran at between 5 and 6 mph, either motoring or motor-sailing and averaged about 50 miles per day, sometimes quite a bit more if the tides and currents were with me. They have a large effect on distance covered on the SE coast where there are many tidal rivers and creeks.
Also, plan on being weathered in for a few days here and there and stops for groceries, repairs, a walk to the post office, sightseeing and so on. There are a surprising number of things which can throw off an schedule. One of the biggest is weather and if you monitor the weather closely, you may find yourself running longer and faster than you had planned to get to a protected or interesting location to sit out a bad spell of weather.
Another thing about schedules: don't have one! They are confining, restrictive and will encourage you to run or stop when you shouldn't and defeat the true purpose of a relaxing cruise.
My wife and I plan on replicating my cruise in a few years, but on Valkyrie, our CD 22. We will run longer than your planned 3-4 four hours a day, however. If we left by seven and ran for 4 hours at 15, we would cover 60 miles that day but that could put us anywhere. If we dropped the hook somewhere in a coastal swamp, which is very beautiful in its own way, we would have the rest of the day, an awful lot of time, to spend at anchor. A respite is nice once in a while, but on a daily basis it would get tedious for us.
Personally, I typically prefer to pick a reasonable destination and run for that rather than stop after a set number of hours. If you run longer each day you could then spend more time exploring some of the great coastal towns along the Chesapeake and ICW. I spent 6 days exploring Charleston and could easily have stayed longer.
One book I found indispensable was THE INTRACOASTAL WATERWAY A Cockpit Cruising Handbook by Jan and Bill Moeller. It gives great tips on anchorages, features and so on. Also, be sure to ask other cruisers for favorite places anchorages, marinas, store and places to see. That will be one of your most valuable resources.
Another great book is PLANNING YOUR ESCAPE which even gives locations and zip codes of local post offices on the ICW so you can have mail forwarded to yourself via General Delivery.
Hope this help.
Regards,
Nick
"Valkyrie"