Example to find the files older than 17 days
The reason to use
-daystart is to make things more natural for human
find performs some rounding. From the man page:
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.
To find files that were accessed exactly 17 days ago (that is: that have been accessed between 00:00 and 23:59:59 on the day that was 17 days ago):