The find command uses arguments like:
-mtime -2
-mtime +2
-mtime 2

There are -ctime and -atime options as well. Since we now understand the differences among mtime, ctime, and atime, by understanding how find uses the -mtime option, the other two become understood as well. So I will describe find's use of the -mtime option.

As you probably know, the find command can run for minutes or hours depending on the size of the filesystem being searched. The find command makes a note of its own start time. It then looks at a file's mtime and computes how many seconds ago the file was modified. By dividing the seconds by 86,400 (and discarding any remainder), it can calculate the file's age in days:

Code:

0 days in seconds:       0  -   86399
1 day in seconds:    86400  -  172799
2 days in seconds:  172800  -  259159

So now that we know how many days ago a file was modified, we can use stuff like "-mtime 2" which specifies files that are 172800 to 259159 seconds older than the instant that the find command was started.

"-mtime -2" means files that are less than 2 days old, such as a file that is 0 or 1 days old.

"-mtime +2" means files that are more than 2 days old... {3, 4, 5, ...}

It may seem odd, but +0 is supposed to work and would mean files more than 0 days old. It is very important to recognize that find's concept of a "day" has nothing to do with midnight.