Answer:

III

Answer	Crossword Clue
III	It's three, on some clocks
III	Jr.'s son
III	Part of some sequel titles

III	Sequel-to-a-sequel designation
III	Sundial notation
III	Sundial numeral
III	Big Ben's three
III	Generational name tack-on
III	Jr.'s son, perhaps
III	Roman prime number
III	A crowd, to Caligula?

III	Sundial figure
III	X minus VII
III	Hank Williams or Robert Griffin
III	Redskins QB RG ...
III	Clock numeral
III	Three, of a kind
III	Roman triad
III	The Third

III	Jr.'s son, sometimes
III	Thurston Howell ..
III	Midafternoon
III	Sequel's sequel?
III	Mid-afternoon, perhaps
III	Midafternoon, in a way
III	Midafternoon, maybe
III	Dynastic third

III	It's right on a clock face
III	Sequel-of-a-sequel number
III	Junior's namesake
III	Second sequel's number
III	"Richard ..."
III	Junior's junior
III	Son of a son
III	Sundial reading

III	XXX divided by X
III	3:00, on a sundial
III	Golf's Davis Love ..
III	Jr.'s namesake
III	Second sequel designation