For example this video is set to link to 139 seconds into the video:
(I put a period into that URL because of the problem I'm about to report)
If you link to this on Xenforo, it ignores the time stamp in the URL. Strangely it does link into the video a bit, but right at the 2:00 mark. Try embedding or even just pasting the URL above into your post (remove the period after the first "h") and you'll see. It should be going to 2:19, not 2:00.
Likewise when I tried changing it to 150 instead of 139, it still starts playing at 2:00.
Can this capability be added? Not sure if this is a bug or a feature request.