When the mobile phone is turned on, is it the time to receive the SMS call reminder or the time when someone calls you?

When someone calls you, it's from a mobile phone. The server will naturally send a message to your mobile phone, but your mobile phone was turned off at that time, and it was received only after it was turned on naturally. Time is the time when someone calls you and the server sends it to your mobile phone. There is little difference.

The time in the text message is the time when the other party sent the text message at that time, and it has nothing to do with whether you turned off your phone or not.