-atime/-ctime/-mtime the last time a files's access time, file status and modification time, measured in days or minutes. Time interval in options -ctime, -mtime and -atime is an integer with optional sign.
n: If the integer n does not have sign this means exactly n days ago, 0 means today.
+n: if it has plus sing, then it means more then n days ago, or older then n,
-n: if it has the minus sign, then it means less than n days ago (-n), or younger then n. It's evident that -1 and 0 are the same and both mean today.
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