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 14.164, one example shows the length of a reel-to-reel tape as 1:12:49; under paragraph 14.58, the length of an audiobook is given as 19 hr., 4 min. An example at CMOS 9.42 (on ISO style for time of day) puts 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.