Four years is a good timeframe estimate to bring that 150mtpa...

Four years is a good timeframe estimate to bring that 150mtpa online.
It took Adani 2 years from breaking dirt to railing and shipping first coal.
I'm not sure if they're at 10mtpa yet... but they've still got two years to ramp up further and have plans to hit 55mtpa.

The constraint for everyone, however, will be skilled labour.
There's simply not enough good people with common sense to get it all done quickly.
I reckon 6-8 years would get another 150mtpa greenfield coal online when allowing for skills shortages.

Of course, companies like WHC & NHC already have mines with nearby infrastructure, whereas the Galilee basin deposits are remote and lack any infrastructure at all. I think we're already seeing a push to open the Bowen Basin deposits before the Galilee. From the top of my head here's what I'm seeing start up over the last year:

Bluff (reopen)

Crinum (reopen)
Cook (reopen)
Broadlea (reopen)
Aquilla
Olive Downs
Moorvale South

Jellinbah North

Dysart East

Isaac Downs

Meteor Downs South

Byerwen

Broadmeadows East
Burton (again?)

There's more exploration deposits that aren't listed, but, the ones listed above are the ones I see that have gone over the line and either are producing or will be in production in the next couple of years. The list includes previously marginal deposits which have trickled down the cost curve after being previously placed on care and maintenance.