A plan laid against time. A schedule is an intention with hours attached.
Late Latin schedula (a small note, a slip of paper), the diminutive of Latin scheda (a leaf of papyrus), itself from Greek schede; a schedule was first the paper the plan was written on, before it named the plan itself.
A plan laid against time — an intention with hours attached, named for the slip of paper it was once written on rather than for the hours themselves.