This tab is available with the Milestone Schedule module is active.

Each job form will have a section available for entering schedule information.  Jobs with estimates will automatically populate Milestone hours with estimated time based on the milestone mapping for all operations on a form.  Hours can be edit by clicking directly on the field.  Edits will not affect costing, only scheduling.  The column next to each line items hours can be clicked to view that milestones schedule for up to 2 weeks.  Notes can be added and the scheduled date entered/edited on the fly.  Items can be marked complete here or on the Milestone schedule board.