There are multiple reasons to switch off your WiFi router at night - from lowering the risk to affect your health or cause insomnia to save planet's energy resources. Most routers do not have this feature, so you will have to do it manually. However, if you own a MikroTik RouterBOARD one, you can easily do it. Moreover, you can even make this automated!
Another alternative is to lower WiFi output power to minimal values. I usually run my router with 100mW output during the working hours, and 8 mW at night. Fortunately, Mikrotik RouterOS also allows to change this setting from scripts, so you can program your own power scheme.