Create a file SAMID.txt and put all the account name in it and execute the command from the current directory.
for /f %C in (SAMID.txt) do dsquery user -samid %C dsmod user -acctexpires
Ex. Today 29-May-2012 and extension has to be done upto 30-JUNE-2012,
Then the no. of days will be 30+3=33
for /f %C in (SAMID.txt) do dsquery user -samid %C dsmod user -acctexpires
Then the no. of days will be 30+3=33