Short answer
Your written quotation confirms the delivery schedule for this dresses commission, including cloth, production and destination. London's proposed visit window is DEC; dates and venues are confirmed individually.
For an event date, your written quotation confirms the schedule for cloth, production and delivery before you order.
London's window
The proposed DEC visit is the planning point for London commissions. Dates, venues and available appointments are confirmed individually in writing as the month approaches.
The itinerary is a proposal: months are planned, dates and venues confirmed individually. Final quotations are confirmed in writing before you commit.