Yes, that's the UNIX timestamp. You can help with this: https://www.unixtimestamp.com/
Btw, I haven't tested this, but it should work.
Sorry, use this code instead:
<xf:if is="$xf.time > 1767225600">
<img src="path/to/image.png" alt="Image" style="max-width:100%; height:auto;" />
</xf:if>
Yes, that's how it currently works. The main purpose of this add-on is to hide these fields for everyone if the administrator decides that they are not needed on their forum.