When I started on it, I took it at night and that turned out to be a good time because it sort of knocked me out.
But when I was on it I noticed that my level of dreams went down.
It doesn't really matter. Celexa has a very long Half life and exact dosage time will not be that important as long as you take it once daily at the prescribed dosage.
If it keeps you awake, take it in morning. If it makes you sleepy take it at night.
It can have either effect depending on the person.