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