My edits to the contrary do not last in the wiki, which is fine, and I think reflect a consensus on the idea that Lost does not have multiple time lines. Yes we have been told that, the show follows a certain logic that implies that but think literally.
Dan Faraday did not originally visit Desmond in the Hatch... he only did so later on, and that was a second time line.
What you have in Lost is not a destiny that cannot be different at all, it CAN be different, it's just that it has to merge again. There is a strong force remerging the change into the original outcome... so if you put off your death for a day, it comes again... but you did change history. But your change will not be chaotic and change future history, instead, it will be erased, someone special like Desmond will wake up with a memory they hadn't had before.