-atime N
True if last-access time of file matches N (measured in days) (see below).

-ctime N
True if last-changed time of file's inode matches N (measured in days, see below).

-mtime N
True if last-modified time of file matches N (measured in days, see below).

-newer FILE
True if last-modified time of file matches N.

# # # See below: # # #
1.   * N is prefixed with a +: match values greater than N
2.   * N is prefixed with a -: match values less than N
3.   * N is not prefixed with either + or -: match only values equal to N