There are a variety of synonyms that can be used to describe the phrase "time to hit hay". Some of the most common alternatives include "bedtime", "lights out", "retire for the night", "tuck in", "go to sleep", "hit the sack", "call it a day", "get some shut-eye", and "turn in for the night". Each of these expressions may be more or less appropriate depending on the situation, but they all convey a similar meaning that it is time to prepare for sleep and rest. Whether you prefer a more formal or informal approach, there is sure to be a phrase that works for you.