A time-quantity is a scalar quantity whose dimension is time-dimension. Conceptually, a time-quantity is an amount [duration] of time. It is constant quantity, not a function or an interval. Like all constant-quantities, its magnitude is given in terms of units of measure. For example, the products of all real numbers and a unit like second-of-time are time quantities.
(<=> (Time-Quantity ?T)
(And (Scalar-Quantity ?T)
(= (Quantity.Dimension ?T) Time-Dimension)))