What people tend to do with this idea is essentially copy and paste the history of South Africa onto the Australian continent. Dutch farmers settle, develop their own dialect, dress, food, and culture, the British conquer the small Dutch colony after it has been populated by settlers for a good while, and then the Dutch Australians migrate into the Outback where they live a rugged and individualist lifestyle. I, for one, thought that it was cool when I first heard of the scenario, but it get's annoying when every single scenario is just a story of Australian Boers. If this trope can be avoided, Australia might be pretty interesting.
I am imagining that the best time for an early British settlement would be between 1606 and 1630. If you settle Australia too late, you will just get a more populous version of OTL's Australia. If you want an interesting and distinct culture to emerge there, aim in the ballpark of 1606-1630. Where do you want the colony to start? It could be on the Eastern coast of Australia or maybe in the Perth area. Since the American colonies were much more appealing at the time and Australia isn't exactly the most hospitable place, your best bet is to turn it into a penal colony but to increase the amount of prisoners sent there. Maybe, have Parliament pass a law stating that anyone who commits a serious offense or gets a prison sentence of more than a year or two will be sent to Australia. You could set up large facilities there where there are vineyards, orchards, dairies, pastures, and ranches just outside of a sizable prison, utilizing unpaid (basically slave) labor from the convicts to produce enough food to feed the growing convict population and to make some money in exports.
Down the line, you could pass a law allowing the relatives of convicts come to Australia permanently or temporarily to visit their loved ones. You would see shops, services, stores, roads, and towns set up next to the prisons for the wives, parents, children, siblings, or other loved ones of the inmates to live in, and if you do something like giving the inmates every weekend off to visit their families we could see some natural increase in the population. These British Australians most likely wouldn't use received pronunciation, nor would they speak with the Australian accent that we know today. Since the inmates would be coming from across England, the different accents and dialects would likely converge and change to form a new accent or dialect that would fit the convicts that speak it.