In fact, it could take more than a day... According to what i have read, it could actually take even more than 3 days to be fully processed.
Indeed it could. But as well as reading about it, you could actually try it. The last transaction I sent with zero-fee was clearing out a mtgox account of about 1 BTC a couple of weeks ago; it took 26 hours to make it into a block. Of course 'fully processed', I presume, is six blocks which is going to happen automatically after the first block and only depends on block-solving variance (which affects everyone and should normally be complete in about an hour).