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For a team of ten this is weeks, not quarters - provided the scope is written down before the work starts and what is outside it is said out loud.
The things that have to happen every day: quotations, orders, invoices, stock, and a website that shows the stock honestly. One database and one subscription instead of four systems held together by exports.
Whatever is already working stays working. Accounting that suits you, a warehouse process people know by heart - these are reasons to keep a habit, not to break it for the sake of a diagram.
The estimate depends on the number of decisions, not on the number of modules. Turning on a module is an afternoon; agreeing on what a discount means in your company can take a week, and it has to be agreed before anything is built on it.
So the first step is always the same: a list of what the system must do, written in your words. Everything after that is measured against it.
A system your people use without a manual, with your data imported and checked, and with a written record of what was decided and why. Plus the parts that were deliberately left out, so nobody rediscovers them later.
If Odoo is the wrong tool for what you described, you hear it on the first call. That happens, and it is cheaper for both sides than finding out in month three.
Half an hour on a call: your screen, your real system, an honest answer about whether the task is mine.