Last posting in the old system on Friday evening, the whole team working in the new one on Monday morning: the cut-over is where all the preparation of an ERP change pays off or takes its revenge. It only runs calmly when improvisation never has to happen.
That takes a fixed scaffold: runbook, dress rehearsal, weekend migration, follow-up.
Runbook and dress rehearsal
The runbook defines every step in advance: who executes which action at what time, which validation follows, who gets informed, what the escalation path is. The rollback path is planned even though nobody wants to use it; knowing it exists makes the decisions over the weekend easier. The dress rehearsal is a complete trial run against real data, and its findings flow back into mapping and validation before the real date is set.
The weekend and the follow-up
Friday evening: logout and data export. Conversion and validation then run against the acceptance criteria defined in advance; Monday morning the logins open. Go-live is not the end: the follow-up reconciles data, monitors the first weeks and retires the legacy systems on a defined schedule. That this holds is documented in an M&A integration: a consulting firm with 80 employees, migrated into a group landscape over a single weekend: Monday morning the business ran normally, no rollback needed. The full approach is described in my article on the M&A cut-over.
Fixed price or time-and-material
A fixed-price cut-over is possible when the scope is clearly bounded. The prerequisites are a solid discovery, a documented scope and a defined acceptance list. Without that clarity up front, time-and-material is the more honest billing model; a fixed price without findings only shifts the risk into change requests.