File was last accessed n*24 hours ago. When find figures out how many 24-hour periods ago the file was last accessed, any fractional part is ignored, so to match -atime +1, a file has to have been accessed at least two days ago.
-ctime n
File's status was last changed n*24 hours ago. See the comments for -atime to understand how rounding affects the interpretation of file status change times.
-mtime n
File's data was last modified n*24 hours ago. See the comments for -atime to understand how rounding affects the interpretation of file modification times.