Q. When an expression like “11 minutes, 52 seconds” occurs in the middle of a sentence (as in “We finished 11 minutes, 52 seconds ahead of the next car”), is a second comma required? If not, why?
A. It may seem reasonable to add a second comma, as Chicago would advise in similar scenarios—for example, after a year when it follows a day: “July 7, 2020, was a Tuesday.” But those two commas work like parentheses, which could be substituted for the commas without changing the meaning of the sentence: “July 7 (2020) was a Tuesday.” The comma in “11 minutes, 52 seconds” acts more like a conjunction, standing in for “and”:
The tortoise crossed the finish line 11 minutes, 52 seconds ahead of the hare.
The tortoise crossed the finish line 11 minutes and 52 seconds ahead of the hare.
A second comma is needed only if the sentence requires it for other reasons:
Beating the hare by 11 minutes, 52 seconds, the tortoise established a new record.
Other expressions that consist of a mix of related units may be handled similarly: “The team’s starting pitcher is five feet, nine inches tall.” But compare the case of a conversion, where the converted units must be fully set off from the surrounding text: “We drove 120 miles (193 km) before running out of gas,” or “We drove 120 miles, or 193 kilometers, before running out of gas.”