The lead time for a client event depends on the scale and complexity. For a small, intimate event (20-50 people), you need at least 2 to 3 months. For a mid-sized to large client event, we recommend 4 to 6 months of preparation.
Bear the invitation process in mind too. Clients have full diaries. Send save-the-dates at least 8 weeks ahead and the official invitation 4-6 weeks in advance. That increases turnout considerably.
Starting early gives you more choice in venues, better availability of entertainment and more room for a well-thought-out concept.