Turn around times at present are very erratic and unpredictable, but I would not be placing any bets on a 309 grant by September, I think that would be a bit unrealistic, 12 months is more likely. If they apply for a 309 and they want to move before grant he would have to enter as a tourist and would be bound by the rules of the tourist visa -eg if he is on an evisitor he can only stay for 3 months and cannot work. No bridging visa available if he applied for a 309. If the 309 is not granted before the tourist visa expires, he would have to leave.

If he travels to Aus on a tourist visa and then decides to apply for a 820/801 onshore then a Bridging Visa A will take effect once the tourist visa expires. Once the Bridging Visa takes effect he has full working rights as he has applied for a 820/801 (working rights are different for BVAs on other visas).

Onshore processing is generally longer than a 309 -recently I've seen 18 months as the norm.

However, hear in mind also that there are changes likely for the whole Lartner Visa process, whereby it is likely that the sponsor will need to get approval before the applicant can apply; this could happen at any time soon, it almost took effect a month or so back but is still waiting for final approval. When it does come in one of the likely effects is that the approval of the sponsor will blow out the timeline, and will take more than 3months -hence making it impossible for the applicant to apply before their visitor visa expires. The (partial) aim is to cut the number of people on bridging visas. There are also rumours of a further price rise in July.

If they are ready to apply now I would do it offshore asap and sit it out in the UK until grant of the 309.

One other option to explore though, depending on the age of the applicant, is for him to get a WHV 417, that gives 12 months in Aus. He could arrive on that and then apply onshore for the 820. Even if the new rules come in he should have enough time to apply in the 12 months, plus he can work at once, under the WHV rules. Once the WHV runs out, if the 820 still isn't granted, he gets the BVA and continues to have working rights.