Now … if you got set deadlines you must decide: either you acknowledge (if that be the case) that the business case in not viable and kill the project before you start losing money, or you downscale the project.
The schedule should be a consequence of planning; planning should be a consequence of previous work (which include the business case). Therefore, once you have decided the project is viable you begin planning and setting a schedule.

The answer is: scheduling is not a profession and can’t live alone, unless you think project management means using Microsoft Project and doing some Gantt diagrams.