The latest that the Dutch could colonise Australia is 1788, i.e. once the British are established on the continent. After this, for one thing the Dutch are rather busy with the Napoleonic Wars until 1815, and the British are fairly entrenched by then.
For another and probably more important thing, history showed that post-1788, whenever anyone else showed an interest in Australia, the British would stop them. This happened in the context of the French in particular - whenever the French looked like establishing a presence anywhere on the continent, the British would set up a settlement in the threatened area to ensure that no-one else got a foothold. To be sure, the British government did not view the Dutch as the same kind of threat as the French. However, regardless of what the attitude in London was, to the people on the ground in Australia, it's clear that they viewed the whole continent as theirs, and did not want to have any other Europeans there. If the Dutch look like setting up a colony - and this is not the sort of venture which will be done overnight - expect some convenient land grants and/or forts to be set up in *Fremantle or *Albany or wherever the Dutch are looking like they might appear.
Of course, as has been pointed out upthread, the Dutch had had over 150 years to colonise Australia if they wanted to, but they really didn't see any point.