Just to add - when in Dimas - I did not ask for a maximum amount of time you can stay w/o having to apply for an extension.
I have heard that a lot of the time the airport can just 'grant' you an extension.
But again - I don't know if there is a "magic" formula here.
I do know that the airport now does 'count' the days you have stayed on the island w/o a residency permit. The max. amount is 6 months.