The App is using your local Date & Time to determine the Timestamp of every collected Response. All this is done automatically, and you don't need to worry about asking your users to provide their Date & Time.
If your device time is different from your local time by more than 24 hours, it will alert you to correct your device time
If your device time is incorrect, you will not be able to collect any Responses.
Response Date & Time is recorded at the time your Response is submitted.