What a Sydney bathroom renovation actually involves
A bathroom is a waterproofing job with tiling on top. Most of what decides whether it lasts happens before a single tile is set. Here is what actually happens, in order.

It starts with a strip-out
Everything comes out, back to the studs and the slab. You cannot build over old problems, so we remove them. On a proper job the waste is gone the same day and the room is made safe.
Then the services
Plumbing and electrical are re-set to the new layout and landed in the wall before any sheeting goes back on. Get the set-out right here and everything after it is simple. Rush it and you are chasing walls open later.
Waterproofing is the part that matters
The wet area is built to AS 3740. The membrane turns up the wall 150 mm, a bond breaker goes into every junction, and the screed falls to the waste. Then it is left to cure before anyone touches it. This is the step bad jobs skip, and the one that fails.
Why it takes 3 to 5 weeks
The membrane needs to cure, and stone and tiles have lead times. A bathroom done properly runs three to five weeks. Anyone promising it in a few days is cutting the cure or the standard.
What to check in a quote
A fixed price after inspection, a licence number, insurance and Home Building Compensation cover on jobs over $20,000, and waterproofing to AS 3740 stated in writing. If those are not on the quote, ask why.