Scheduled shutdown -h hh:mm command doesn't work

[fall4you]

hey folks, i tried to shutdown my maya MATE with sudo shutdown -h 23:00, but i got no response after hitting enter except a blinking cursor.
sudo shutdown -h +30 doesn't work either, but i can shut my system down with sudo shutdown -h now.

the shutdown command used to work perfectly with maya cinnamon and ubuntu 10.04, well, as i recall it doesn't work with ubuntu 12.04 either. i would've had cinnamon but x keeps freezing when browsing with firefox, the same thing happens with ubuntu 12.04. i guess it's all gnome 3's fault 'cause MATE doesn't seem to have this freezing problem.

so any ideas?