The words "you" and "your" are all singular. The word "we" here does not include Peter. (See: [[rc://en/ta/man/translate/figs-you]] and [[rc://en/ta/man/translate/figs-exclusive]])
Cornelius is referring to the day before the third night before he is speaking to Peter. Biblical culture counts the current day, so the day before three nights ago is "four days ago." Current Western culture does not count the current day, so many Western translations read, "three days ago."
# praying
Some ancient authorities say "fasting and praying" instead of simply "praying." (See: [[rc://en/ta/man/translate/translate-textvariants]])