All advice / Planning and process
The short answer
A bathroom renovation is usually measured in weeks rather than days. The exact timeline depends on the room, the scope, product availability, approvals and what is discovered once the old finishes are removed.
A reliable programme should explain the sequence of work and identify decisions that need to be made before the job starts. That is more useful than promising an attractive number of days before the room has been measured.
The stages that shape the programme
Planning covers the measure, selections, scope and written quote. The site work then commonly moves through protection and demolition, plumbing and electrical preparation, waterproofing, tiling, installation of fittings, finishing and clean-up.
Some stages depend on the previous one. Waterproofing needs the right preparation, and later finishes depend on completed and properly cured work. A rushed sequence can create more risk than a realistic programme.
How to reduce avoidable delays
Confirm the layout, fittings and tile choices early. Ask which items the renovator is ordering, when they are expected and what happens if a selected product is unavailable.
Your quote should also explain how changes are approved. Keeping decisions in writing helps the homeowner and the renovation team work from the same scope.