Why is set automatically greyed or disabled in iPhone
Time in your iPhone is instantly set while using Network Time Protocol (NTP). This can be a protocol accustomed to synchronize time on computers more than a network. Should you disable this setting, your iPhone won’t be able to help keep the right time.
On the majority of devices, the “Set Time Automatically” choice is switched on automatically. This setting uses your device’s location to look for the time zone and sets your device’s clock accordingly. If you’re not someplace where your device will get an indication from the cellular or Wi-Fi network, your device’s clock won’t update.