For those who are trying to make or schedule an appointment at USCIS inside the United States, and always getting this message below
"There are no available appointment slots for this date. Please choose another."

I wanted to share my own feedback and tips, after getting frustrated trying every single day of the week.

I tried a couple of time on Monday morning
7.00 AM (Pacific Time) - Nothing
7.30 AM (Pacific Time) - Nothing
8.00 AM (Pacific Time) - Nothing
8.30-9.00 AM (Pacific Time) - Finally the USCIS appointment schedule calendar open, I was able to book my appointment at earliest 2 week ahead!

Hope that helps

Good luck!