An ERP programme is a process project wearing software.
The system is the last part. What takes the time is agreeing how an order becomes a commitment, when a cost lands, who may approve what and at what value, which entity owns which balance, and what the chart of accounts is actually for. Every one of those is a business decision that configuration then records. Organisations that treat it as an IT installation discover the decisions anyway, during testing, when changing them is expensive.
Master data is where programmes are lost.
Customers, suppliers, items, cost centres and employees usually exist in several places with different keys, different spellings and different rules about what is current. Nobody owns them, because ownership was never assigned. Reconciling that is unglamorous, it is on the critical path, and it is the single most common reason a go-live date moves.
We start with the operating model, then configure.
Current process and system landscape, the decisions that have to be settled and who settles them, a target process design with the exceptions written down rather than discovered, data ownership and a cleansing plan, then configuration against an agreed design. Integration and reporting are designed alongside, not bolted on when the core is finished.
What you are left with.
A configured system, a documented process design that matches it, reconciled master data with a named owner per domain, a tested cutover with a rehearsal behind it, and people who were trained on their own process rather than on a generic module. Plus a written list of what was deliberately left out and when it is due.