Hyphens, En Dashes, Em Dashes

Q. Would you hyphenate the phrase “day and a half”?

A. No, unless you are using it to modify a noun (not always the best idea):

It took a day and a half to throw all his stuff onto the lawn.

The day-and-a-half class required hip waders, a claw hammer, and a signed liability release.

[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]