-atime n 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. -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.
but see also:
-daystart Measure times (for -amin, -atime, -cmin, -ctime, -mmin, and -mtime) from the beginning of today rather than from 24 hours ago. This option only affects tests which appear later on the command line.
In summary, use
find -mtime +1 to find 2 day old files.