I adore the cape but March is very cold generally, often rainy and windy, not much of interest open.

My first visit to the Cape was in March, after a week spent at a conference in Boston. We drove all the way out to Provincetown and spent the night there. I promptly fell in love and have been back many times. A lot of the places are closed up because as jubilada said it will be cold and windy. Lots of snow too. But I'm from the south so was completely enchanted. We enjoyed the drive and just seeing the scenery. We stopped at Plymouth on the way in and drove around Hyannis a bit on the way back, but mostly just enjoyed looking around. If you want a bit of fun and a quick stop the "tour" of the Cape Cod potato chip factory is interesting. It's a self-guided "tour". You basically just walk through the building and watch the process through windows.

If "PM" means early afternoon, you should drive from Boston to Chatham, have a nice dinner and spend the night. Saturday morning, you can explore Chatham and Eastham and drive back toward Sandwich on scenic 6A ("King's Highway") not to be confused with US 6. Have lunch along the way. Explore the side roads. Go west from Sandwich on MA 3 to return to Boston.

BUT jubilada is right that it will be cold, possibly very cold, there will be no leaves on the trees until May 1 (it is colder than Boston) and much of the restaurant/lodging infrastructure won't even open until near Memorial Day (last weekend in May).

You should do it, but drive the whole way out to P'town and spend the night. That way you can see and enjoy the National Seashore. And have a leisurely drive through Eastham, Chatham, Sandwich on the way back. But, as mentioned the weather might be cold.

Late March is often still winter here. You can be lucky and get a high of 50 - or you could get a significant snow storm. (The blizzard of '88 - with more than 2 feet os snow was in late March.)

And Boston can be enough colder than NYC to make a difference. In late April I did a one-way turnaround for a business meting and got stick in Boston overnight. Although it was around 50 in NYC the rain in Boston turned to sleet by 6 pm - and the airport was a disaster with a flights delayed for hours and a bunch cancelled.

So before heading to Cape at that time of year, I would look at the weather forecast carefully.

All wonderful and helpful suggestions. Thank you. Will consider ourselves fully advised about the weather in late March ! I love a good storm if I am indoors but could be dicey if on the road.

If you are cognizant about the weather and get lucky I agree that you should drive all the way to Provincetown to make the most of your trip. Eat at the Mews. The Admiral's Landing is a year round B&B, one of only a few.