I think I figured it out.
add -display :0.0 after the app you want to launch at a specified time.
[archie@localhost ~]$ at 12:00
warning: commands will be executed using (in order) a) $SHELL b) login shell c) /bin/sh
at> ktorrent -display :0.0
job 14 at Fri Nov 18 12:00:00 2011
I hope it also fix it up for you.