the subject pritty much explains it
Not really, as there are different techniques on different OSes and you failed to mention yours. For Win9x (incl. ME) you can use the
choice command with the /t switch (default value after nn second; max 99)
CHOICE is not available on shipped copies of NT machines, so you can use PING (ex. ping -n 21 should be close to 20 seconds).
8-)
Note: PING is the better of the two as it does not tie up the CPU with wasted cycles.