GGB Honestly: it depends on your file, and anyone quoting a firm week-count before seeing that file is guessing. The sequence itself is fixed — feasibility, licence route and approvals, site and design, fit-out and kitchen build, pre-opening, then opening on the numbers — but each phase's length is governed by different things: how quickly you accept what the feasibility data says, the authorities' own review cycles and the completeness of your submissions, the handover condition of the unit, the complexity of the kitchen, and staffing lead times. Plan the sequence and manage the governors, and the date becomes an output you can defend rather than a number you were sold.
From The Restaurant Opening Timeline — What Actually Governs It — the full reading, with the method behind this answer.