NOTE: I am not a migration agent, you should seek professional council if you need help :NOTE
This was my experience with bridging a/b visas (and should not be construed as professional advice or in any way authoritative, see above comment about seeking peofessional advice)
When my 457 was running out and I had a business trip scheduled (literally on the day my original visa expired), the agent my company used submitted the 457 renewal (which also grants a bridging A visa); For the bridging B visa, they had me go and file in person; The bridging B visa can apparently be granted on the spot if you have travel that is less than two weeks away (at least thats what the senior immigration agent said, but depending on who you end up talking to they can get very strict, mine said that because I was there at 9am ad my flight was at 11am two weeks later that they wouldn't grant it on the spot - I had the misfortune to get an agent on his first day, who first claimed that there was no way I could file for the bridging visa in person if I was a 457 holder) - That said, it was granted the same day when it was passed along - The paperwork I was given to file was not simply the standard pdf, it had extra attachments like plane tickets and letters from my company covering why they were sending me, etc which I would assume helps answer questions like "why can't you just hang tight for a bit and not leave the country"
If you are in a tight spot, speaking to a migration agent is the best option so you get informed professional advice and avoid anything that might impact your application at a later date