It depends on what you are planning to build.

The fastest I experienced was about 4 months- but that is rare now a days.

A beach house my family built as owner builders took 2 years to get planning approval!! why?

The water front acreage was zoned Environmentally Sensitive- with a creek running through, very poor soil condition and the list went on. After two years the zoning changed to General Residential and my lemon turned into a million dollar site. The neighbours were the ones to benefit my hard work. I faced the whole council- from Mayor down to engineers. But I love design and engineering and my data on geotech matters flabbergasted them. Council was relying on assumptions, I presented facts.

The approval allowed us to build the beach house from where we saw migrating whales and the Sydney to Hobart race!

In those days only councils could issue Building Approvals after Town Planning approval.

We designed 6 metre deep screw in foundations ( new stuff then) built a drainage system wrapping around the back to drain water. The very low cost light weight house with a dual occ option or BnB had its structure which could be loosened or tightened depending on the soil movement.

Well we never had to adjust one bolt- so much for Council's engineering conditions. And the building faced storms and an mini tornado with no consequence.

And being an owner builder felt great!