When's the best time to drive from Philly to CapeCod on a Tuesday. And best route?
Then taking the ferry to Nantucket, would like to arrive at dusk.

You could have put all your questions in one post. I sent a reply to your other post.

As for the ferry over to Nantucket, I guess you plan to leave from Hyannis? Do you plan to take the fast ferry or the slow ferry? Are you planning to take your car? The summer is a very busy time and reservations are needed at times, if you plan to take your car you must make a reservation.

If you take the (from Hyannis) slow ferry, the evening time leaves Hyannis at 6:30pm or 8:00pm. The slow ferry takes 2hours,fifteen minutes.
The fast ferry (from Hyannis) afternoon/evening times 4:30pm or 7:15pm. This ferry takes one hour.
Parking for two days cost me around $50.00. They do have a shuttle that will take you from your car to the ferry. I always call ahead of time to see what lot I should park my car. Plan to get there at least one hour ahead of departure time so you can park, get the shuttle and buy your tickets.

I would Check to see if you need a reservation for the ferry.

Enjoy!! I just spent a wonderful time on Nantucket, I love it more each time.

I am going to assume that if you want to arrive at dusk, you already have a reservation on the 8 PM Steamship Ferry Eagle, since the MV Nantucket leaves as Lmw_20 says at 6:30. If you don't have a car reservation already, you are almost certainly toast, though you can take the 7:15 fast ferry.

The only route choice, since you are stuck with I-95 is between the GW Bridge and the Tappan Zee. I would expect you to be passing NYC noonish, so I would risk the GW Bridge, having monitored AM radio station 1010 WINS to be sure there are no wrecks or construction delays.

Other delays may come around Branford, CT, just east of New Haven, where construction has been ongoing for years, and Providence, which is much better than it used to be.

The roughly seven hour timing on Google maps is a fiction since it allows no time for toilets, gas, food, or traffic delays. On the Cape, do not be tempted by what looks like a more direct route from the bridge to Hyannis on Route 28. It is clogged with strip malls and traffic. Take US 6, get off at marked Hyannis exits.

If you have a car reservation, you MUST be in line at least half an hour before sailing or they will give away your reservation to a standby. As above, you ought to allow an hour to park, take a shuttle, and get walk-on tickets for either ferry. I would not expect you to need a reservation on the fast ferry on a Tuesday. The food on the slow ferries is decent, esp the chowder, if you find yourself running late and not able to grab any supper. It isn't very good on the fast ferry. Both are expensive.

By the way, the schedules change for the car ferries after Labor Day, so you need to let us know if that is when you are planning to go.

I just want to comment on the route or drive time from Philly to the Cape. I live in central coastal NJ (Toms River area), trust me when I say it takes me 6 hours with bathroom breaks to get to Hyannis. This is leaving between 3-4am. Sorry, but I have learned my lesson and will not leave at any other time.
I rather drag my butt out of bed early and know I will not sit in traffic and I have the whole road to myself!

My parents came down to Southern NJ from the Cape last week and were recommending that travelers stay off I-95 as much as they can through Connecticut. It is a mess. Take the Merritt Parkway.