Organize the checklist into four windows. Day 1: live announcements to both teams, one-page talking points for customer-facing employees, payroll and banking confirmed, customer-facing systems verified. First 30 days: top twenty customers contacted personally, one named owner per significant account published internally, knowledge interviews with long-tenured people, integration model chosen. Days 31 to 90: back-office consolidation, joint account reviews, revenue assumptions rewritten as named account lists. Days 91 to 365: systems, branding, compensation, and territory changes.