just cronjob:
echo "0 23 * * * uci set wireless.@wifi-device[0].disabled=1; wifi" >> /etc/crontabs/root
echo "0 7 * * * uci set wireless.@wifi-device[0].disabled=0; wifi" >> /etc/crontabs/root
echo "root" > /etc/crontabs/cron.update
/etc/init.d/cron enable
/etc/init.d/cron start
/etc/init.d/cron restart
wireless.@wifi-device[0] probably is radio0, wireless.@wifi-device[1] probably is radio1 (this is by convention)