The word "days" in the phrase "five business days" does not require any punctuation. In general, when indicating a duration, such as "five days" or "three weeks," there is no need to include punctuation after the unit of time. However, if you were to use an abbreviation, such as "5 days" or "3 weeks," then a comma is sometimes used as a separator (e.g., "5 days, 3 weeks") but it is not necessary and could be considered a matter of style or personal preference.
