Correct use of endash in range of minutes

Question

I am currently working as a web developer, and will occasionally be asked to update a website. A "client" just send me an update containing this text:

A 15-30-minute waiting-period is required after each injection is given.

Notice the use of 2 hyphens, which I am sure is not the correct style to use. I have been taught to use en dashes to separate ranges of values, such as 15–30, and also to add word spaces if I feel the en dash runs into the words on either side. However, I also vaguely think I was taught to put a hyphen between a phrase like this: "… going on a 30-minute walk."

If I follow both of these "rules", I will end up with a sentence that looks like this:

A 15–30-minute waiting-period is required after each injection is given.

As you can see, this only differs from the original because of the en dash between 15 and 30. However, I still think that looks weird. I think that it ideally would look like this:

A 15–30 minute waiting period is required after each injection is given.

Note: I also removed the hyphen between waiting and period, as I don't think that should be there either.

Questions

Question 1: What is the proper way of rendering the first part of the sentence? Is it an en dash between the numbers and then no hyphen between the last number and the word minute?

Question 2: Should the words waiting and period have a hyphen between them?

The reason that this question doesn't answer my question specifically is that while I know the differences between hyphens and dashes, the way the sentence is composed lends itself to confusion. Having an en dash in the word before a hyphen seems rather strange.

• What is the difference between hyphens, en dashes, and em dashes?

Thanks!

Answer 1

You are right on both counts and I like your version of the sentence the best. There is no need for "30-minute" but it is acceptable and "15- to 30-minutes" is a fine suggestion by @FumbleFingers. I used thepunctuationguide.com as my reference.

Answer 2

You can avoid the number clumping by reframing the sentence in this way:

A waiting period of 15 to 30 minutes is required after each injection is given.

If you want to retain the structure as given by the client, I would endorse FumbleFingers's recommendation:

A 15- to 30-minute waiting period is required after each injection is given.

Phrases of the form "15- to 30-minute" are discussed in The Chicago Manual of Style, fifteenth edition (2003):

7.89 Hyphen with word space. When the second part of a hyphenated expression is omitted, the hyphen is retained, followed by a word space.

[Relevant examples:] fifteen- and twenty-year mortgages, five- to ten-minute intervals

Notice that in both of these examples the unit of measure (year in one, and minute in the other) remains singular.

Whether to use numerals rather than spelled-out numbers is a separate issue; but in the case of measurements involving time, you can find considerable support in style guides for using numerals even for numbers under 100.

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One of the primary roles of an en-dash is to indicate a numerical range, such as a range of page numbers. Professionally produced indexes in the United States typically use them, so you'll get entries like this one from the index to Christopher Hitchens, Arguably (2011):

fascism, 195, 196, 198–99, 214, 334–34, 342–45, 550, 588, 635, 671

Another important role that en-dashes sometimes play is in indicating that the final element in a compound phrase involving a multiple-word proper name extends across the the letter space between word to comprehend the entire proper name, as here:

Civil War–era popular songs

In general, however, I consider it very unwise to slip an en-dash into a compound phrase that also contains one or more hyphens, as you suggested doing with

15–30-minute waiting-period

and expect readers to recognize the difference in length of the punctuation marks and the difference in sense that the en-dash and the hyphens are supposed to convey.