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Should there be a comma before "X min each time" in sentences like:

Wash the sections with PBS twice for 5 min each time.

I found examples with no comma:

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And examples with a comma:

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Maybe it could be omitted in terse technical language? But in normal language, would the comma be necessary?
Would the situation be different If we used "for 5 min each time"?

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    Maybe it's just sloppy writing. Note the end of the second line of the first example: "was with PBS 3 times". A comma or for certainly improves readability. – JavaLatte Aug 6 '16 at 9:17
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    My first thought was that 'wash' should be 'watch': “Watch the sections with PBS twice 5 min each time” – Alan Carmack Aug 6 '16 at 13:23
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Wash the sections with PBS twice for 5 min each time.

I would say that this sentence is fine because of the use of "for." It could be written as follows, and in this example a comma is required:

For 5 minutes each time, wash the sections twice with PBS.

As for your other sentences, I'd say that they are just poorly-written. However, in terse writing there aren't really any rules to be followed – what is written is (close to) the minimum required for understanding. The most common example of this is probably Headlinese:

  • Forms of the verb "to be" are omitted.
  • Articles are usually omitted.
  • Most verbs are simple present tense.
  • The future is expressed as "to" followed by a verb.
  • In the US (but not the UK), conjunctions are replaced by a comma.
  • A long word is sometimes replaced by a shorter word with not quite the same meaning.
  • Country names are often used instead of their adjective form.

If I wasn't writing them tersely, I would probably write the sentences in your question as:

Wash the slides with PBS three more times for 5 minutes each time.

Add Strepavididn HRP for one hour, then wash with PBS three times for 5 minutes each time, and then wash with deionized water for 2 minutes.

Wash with PEM twice for 5 minutes each time.

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