Because the VA line is outside, ie, in the open zone, its playing it very close.
Its very hard to say for sure, how long it will take from deplanning, ie, getting off the DL flight, walking to immi, doing the Smartgate, going to baggage claim, and then getting out into side A or side B, and then getting to the VA transfer bus service desk, getting the small long strip of what they call a bus pass, having to line up and wait for the bus in the queue...
Your choice ultimately...
Personally I would go for the first or second flight the next day.
On one of my return trips from NZ, when AirNZ were still a partner of VA, it was a shock to see the queue for the VA transfer bus.
I instead got onto the Sydney Buses bus to the domestic terminal to get my flight to Adelaide.
The VA transfer bus also does not drop you off into the T2 secure area, but drops you off outside the front of (VA's) SYD T2.
Then you have to navigate the terminal to get through domestic security, and then then onto the gate area.
It would be different if the VA bus departed from a zone at T1 less people from all of VA's flights get on, but the VA transfer bus collects all and sundry of VA's partner airlines...