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/1Y4nWizG5ebNgUqHyHhbknE1gc2vnReXV

initial 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.