Hyphens, En Dashes, Em Dashes

Q. Do you recommend using a hyphen when spelling out the time of day?

A. Our rule is to reserve hyphens for the naturally hyphenated cardinal number:

eight forty-five; five fifteen; three thirty

But add a hyphen when the time of day precedes and modifies a noun, unless part of the expression is already hyphenated:

three-thirty train; eight forty-five appointment