Looks like you're using the default html template:
The data is displayed with:
<td width="100%" bgColor="#FFFFFF"><i><b>Time:</b> $nimts_exp, <b>Arrival Time:</b> $arrival_exp, <b>Assigned To:</b> $assigned_to, <b>Count:</b> $count</i></td>
The time variable is $nimts_exp which is consistent with your picture. $nimts: indicates the message timestamp, when it was originally sent.
emailgtw Advanced Configuration - CA Unified Infrastructure Management Probes - CA Technologies Documentation has the full set of variables and their descriptions.
I'd suggest using $supptime_exp: indicates the readable form of $supptime. $supptime: indicates the timestamp of the last suppression of this message.