Any U.S. Post Offices open Saturdays for counter service?

Is there a local U.S. Post Office that provides counter service on Saturdays? I have an item that requires special USPS handling. It would be great if I could get it in the mail before Monday.

(I’ve Googled and found a 3rd party site that says the Hadley St. post office is open until noon. But, I’m having trouble locating something official that confirms it.)