alright let's try exactly as it works for me:
fill /etc/crontabs/root
with (adjusting the times per your needs):
# enable all LEDs at 7am
0 7 * * * /bin/echo "1" > /sys/class/leds/green:lan/brightness ; /bin/echo "1" > /sys/class/leds/green:wan/brightness
# disable all LEDs at 9pm
0 21 * * * /bin/echo "0" > /sys/class/leds/green:lan/brightness ; /bin/echo "0" > /sys/class/leds/green:wan/brightness
hopefully that should do it