Definition

Day 1

Closing day — the operational handover from seller to buyer and the start of integration execution.

Day 1 readiness is a programme in its own right: legal handover, customer and employee communications, HRIS and email cutover, payroll, banking, brand. The bar is 'no customer-facing disruption'. Day-1 issues are the visible failures of an under-prepared integration; the invisible failures show up in months 4–12.