http://www.iphonehacks.com/2017/11/ios-11-3-will-show-pop-explaining-wi-fibluetooth-toggle-functionality-control-center.html



As mentioned, toggling Wi-Fi and Bluetooth off from the Control Center only disables certain features of the two radios temporarily. While the pop-up from Apple says that Wi-Fi/Bluetooth will automatically turn on tomorrow which is 5 a.m. as per Apple’s definition. The ‘tomorrow’ scenario also has a few other conditions as well. If you go to a different location, your iPhone/iPad will automatically connect to a known Wi-Fi network there. Similarly, if you restart your iOS device, it will automatically reconnect to a known Wi-Fi network even if you previously disconnected it from the Control Center. The same conditions also apply for Bluetooth.