Q. I am preparing an online archive. Many of the items are audio or video recordings. I’ve fruitlessly searched CMOS for the proper way to indicate the total time of a recording—for example, thirty-five minutes and thirty-three seconds. 35 min. 33 sec.? 35m:33s?

A. There are various accepted stylings. At CMOS 14.264 (“Recorded Readings, Lectures, Audiobooks, and the Like”) one example shows the length of a reel-to-reel tape as 1:12:49, and another shows the length of an audiobook as 13 hr., 6 min. An example at CMOS 9.40 (“ISO Style for Time of Day”) suggests the option of putting a zero in front of a single-digit measure of time: 09:27:08.6 = 27 minutes, 8.6 seconds after 9:00 a.m. Based on all these examples, you could use either 00:35:33 (to clarify that it’s 35 minutes, not 35 hours) or 35 min., 33 sec.