eBay auction end time calculator

#!/bin/sh
# Requires dateutils
# script by The Lightning Stalker 2014
#
if [ -z $1 ]; then
echo 'Show time left until end of auction in hh:mm:ss'
echo 'Input must be actual eBay time (Pacific timezone)'
echo 'Use it like this: ebaytl.sh YYYY-MM-DDTHH:MM'
echo 'For example $ebaytl.sh 2014-09-14T14:29'
exit
fi
ddiff --from-zone America/Dawson -f '%H:%M:%S' now $1