Naturalized US citizens or friends thereof: How much time before your Oath Ceremony did the notice with the date (N-445) arrive?

I had to postpone my first naturalization oath ceremony because I was out of the country. I have scheduled a trip back to the US for two weeks specifically because I was told that my ceremony would be on the last Friday of April, but I haven’t received any notice of the ceremony date yet. Help, I’m rather worried.