As per my understanding, there is no such phenomenon that a time/date stamp appears when someone mouse over a comment balloon in Reporting Services. And based on my research, this can be appeared in word document. So I’m confused which products are you involved.
If this issue is regard to word document, I will move this thread to Microsoft Office forums. It is appropriate and more experts will assist you.
If there are any misunderstanding, please elaborate the issue for further investigation.