Looks like you can win, even if you send your bid a lot later than the initial bid; see round #535:
http://blockchain.info/address/1Y4nWizG5ebNgUqHyHhbknE1gc2vnReXVinitial bid was made 2012-12-12 17:15:08, the winning bid (me :-) was at 2012-12-12 17:43:42, ie almost an half hour later.
Hmm.. however, I would guess you get better chances, if you bid asap after initial bid. But the difference might be smaller than one would think.
Correct, you can win ANYTIME you have the highest bid in the first block. Blocks do take a long time, it's not that hard to get 30 minutes or an hour (although it is less common) between blocks. In your case the initial bid was sent immediately and your bid 30 minutes later both made it into block # 211953. That's just exactly the game. The initial bid might be sent and ten seconds later it is in a block or it might drag on and on and on. You never know.
If you send immediately then you have the maximum chance of getting included with the initial bid but you also have the maximum chance of being outbid. So, again, that's the game.