According to the Puritans, at what time did the Sabbath start and end?

In college, many of my Presbyterian brothers wouldn't study on Sunday, seeing that as a violation of the Christian Sabbath. But I heard that at least one of them, if he had a test on Monday morning, would wait until midnight Sunday night, and *only then* study for the test for a few hours before going to sleep. The strict use of midnight in my brother's Sabbath observance has led me to wonder about the *timing* of the Sabbath in Puritan sabbatarianism more broadly. So, I'd like to know – **at what time did the Sabbath start and end for the Puritans?** I'm open to responses from both English and American Puritans, up to the 18th century. If there isn't agreement, then I'd like an overview of common positions.