Hi Alberto,
The short answer is that it's not possible to have multiple dates on the window, on the same field.
The reasons are somewhat complex as to exactly why, but suffice to say that changing it would be quite a serious step at this stage, and not one I'm wanting to make before at least NetTalk 5.
So what you'll need to do is make another field (a local field) to hold the second copy of the date.
Sorry.
Cheers
Bruce