Backlight doesn't turn on after 10 pm even though the option in the settings is set to 'ON' on touch!
i am guessing you have your sleep time set to 10pm until sometime in the morning. if so, at least for my watch, this disables the backlight which i personally like. try adjusting your sleep hours and i am guessing your will have the backlight work at a later hour if you make the sleep time later.