。
Make sure you're here by the appointed time.
Literal
Promise [gen-の] time [by-までに] without-fail here [to-に] come [purpose-ように].
A close variant differing only in the directional particle: へ (marking direction) versus に (marking goal/destination). Both are grammatical with 来る; the difference is subtle — へ emphasizes motion toward, に emphasizes arrival at. In casual speech the distinction is almost invisible.