Some projects must begin with urgency to solve a critical problem, and others have the flexibility to start when resources are ready.
Sometimes it's necessary to plan iteratively, based on known factors at the time. This process can be repeated many times until the desired state is reached.
Even if it must be abbreviated based on what's known at the time. This will be a wayfinder for the Project Team once you've resolved the initial fire.
Not only will this limit confusion around who is truly accountable for completing the work, it will save time later trying to rework something completed under the wrong ownership.