Hello,
The timestamp seen in the Messages tab is generated by the router when it receives an SMS message, so it displays the arrival time. However, for an SMS message to arrive it usually takes no more than 1 second, and WebUI measures the time received in seconds, so there wouldn't be enough accuracy to calculate the delta. Unfortunately there is no setting to configure which timestamp is shown.
Let me know if any more information is needed.
Best regards,
DaumantasG