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
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.
Published 30 August 2019