How long did it usually take to sail from Philadelphia to Boston in the 1700s? I've been able to find lots of sources talking about sailing time between England and the colonies, but I haven't found anything yet about sailing time between the colonies.
The problem you have with such a journey, at the time, is there is no direct way to travel between the two. From most texts I have read about shipping to Philadelphia entry is only through the Delaware River that makes up the border of New Jersey and Delaware. When reading about Howe's exit from Philadelphia this is prominent as the Colonials were attempting to blockade the river with ships. To get from Boston you would need to go down the coast and then travel up the Delaware River.
With that in mind I looked at first to see if there was anything that showed how fast ships could travel at the time.
I did find a site asking such a question a few years ago, on the American Patriot blogspot where they extrapolated the speed of sailing ships. Which is really needed to answer this, see the site for how they determine that rate. The speed they come up with is 8.3 mph, I will use that to base my answer.
If you look on Google maps you can get a straight line distance of roughly 310 miles, land based. That is by current roads, which is not what you would have even had at the time. There are numerous texts that note how long it takes to travel up and down the East Coast, no need to cover that. Using Google Maps you can drag the roadways along the coasts and get a closer approximation of 603 land miles (or 524.6 nautical miles) which gives a travel time of about 63 hours.
As a check if you look up the Port Distances between Boston and Philadelphia you get 535 nautical miles, which is very similar to the Google Map conversion I just did.
So, if the trip was a straight shot, without stopping (which I highly doubt) you would be looking at 63 hours/ 2.5 days of travel time to get from Boston to Philadelphia. As noted below this is not how you would travel, pulling into ports to stop, avoid storms, or trade along the way would definitely increase your travel time.
Did a google map thing and followed the coastline as close as possible, came out to 700 miles give or take. That is 608.something nautical miles, so call that 600 for easy math. More googling shows a few papers citing 4.something knots as the average speed of the average ship of the time. At a speed of 4 knots (4 nm/hr) call it 100nm per 24 hr period. So about a week. Add in delays due to waiting for a harbor/river pilot, the proper tidal stage, bad weather, wind in wrong direction (speed towards destination when tacking drops dramatically even though you can be moving fairly fast), etc. and call it a 7-14 day sail.