A small internal tool with stable requirements often shows a usable build in 6–10 weeks. Multi-org systems with history and APIs more often take 3–6 months. Unstable scope extends the calendar.
Small tools (accounts, one main flow, a few reports): often 6–10 weeks. Systems with approvals, many roles and external APIs: commonly 3–6 months. Those are magnitudes when scope is roughly stable — not a contractual slogan.
Apps add store review. WMS adds a floor walk and a trial loop. Software, mobile and warehouse are three critical paths that happen to share a vendor.
You can add engineers on independent modules. You cannot add people to a partner who issues a test book next Thursday. Write that wait into the plan.
Parallel work helps. Discovery and counterparty interfaces do not compress the same way. Waiting for a finance test book is still waiting.
Usually scope was never frozen, or acceptance is "leadership will have another look". Put acceptance in the memo or test week cannot end.
Three must-have functions and one explicit non-goal. That is enough to sketch a first phase.
List what must go live and what can wait. We will put a first-phase calendar on that list at /en/contact/.