/system leds> settings set all-leds-off=after-1h
failure: This feature is not supported on this board!
But adding the 'dark-mode=after-1h' logic to below should be possible as you can always disable the leds manually, which is not what we want because we only want them to be disabled after 1h uptime (for installation verification purposes)
/system leds> print
Flags: X - disabled, * - default
# TYPE INTERFACE LEDS
0 * interface-activity ether1-wan eth1-led
1 * interface-activity ether2-master-local eth2-led
2 * interface-activity ether3-slave-local eth3-led
3 * wireless-status wlan1 wlan1-led
4 * wireless-status wlan2 wlan2-led
/system leds> set [find] disabled=y