TheInstall the NTP daemon on Arch Linux ARM image from http://www.raspberrypi.org/downloads usewith systemd.:
sudo pacman -S ntp
sudo systemctl enable ntpd
sudo systemctl start ntpd
Also make sure your timezone is set correctly, in my case:
sudo rm /etc/localtime
sudo ln -s /usr/share/zoneinfo/Asia/Tokyo /etc/localtime