A point in time denoted in the planning horizon of the master scheduling process that marks a boundary inside of which changes to the schedule may adversely affect component schedules, capacity plans, customer deliveries, and cost. Outside the planning time fence, customer orders may be booked and cha nges to the master schedule can be made within the constraints of the production plan. Changes inside the planning time fence must be made manually by the master scheduler. Synonym: Planning Fence. Also see: Cumulative Lead Time, Demand Time Fence, Firm Planned Order, Planned Order, Planning Horizon, Time Fence.