Soap Sync service, Start time - End time issue

Please help me with this

how to pesist Duraton of Sync message processing?

This is a synchronous scenario, SOAP, sebservice, then I need statistics of processing time. Like this.

Then I can see Start Time and End Time different. And Duration is calculated right.

Image may be NSFW.
Clik here to view.

If the process sent more messages, then in pimon Start time and End time for old records become equals, and duration is 0.

Same Message ID

Image may be NSFW.
Clik here to view.

Image may be NSFW.
Clik here to view.

Thanks for your help