In reference to centuries, when should I use a hyphen with early and late?

Note: This post relates to content in the eighth edition of the MLA Handbook. For up-to-date guidance, see the ninth edition of the MLA Handbook.

MLA style generally hyphenates elements of a compound adjective and does not use a hyphen for a noun phrase.

a poet of the early nineteenth century

an early-nineteenth-century poet

theater in the late twentieth century

late-twentieth-century theater

A compound with mid is trickier, in that there is more than one way to style it.

At mid-century the practice flourished.

In the mid–eighteenth century [use an en dash] the practice flourished.

In early- and mid-eighteenth-century salons the practice flourished.

Or you might decide to leave open a mid compound you would otherwise hyphenate.

In the early and mid eighteenth century the practice flourished.