A while back I had said that because of S -Voice (competing with Google's Google Now), Samsung's take on Jelly Bean might take more time than HTC . If the rumor mills are to be believed S3 owners might see the new version by August.
I am really interested to see how they incorporated Google Now in to touchwiz because I just don't see Samsung give up the "long press" home key to Google Now. For now the best solution that comes to mind is Google Now being a separate app or worse they just dont include it at all.
A thing to note, I have had a Samsung Captivate before and know the target for Froyo went from "just a few months" to "Dec 2010" to sometime late in 2011 after ATT added their delay so I would lean towards them not making this deadline.