  We present a scaling theory for the entanglement spectrum under an external
driving. Based on the static scaling of the Schmidt gap and the theory of
finite-time scaling, we show that the Schmidt gap can signal the critical point
and be used to estimate the critical exponents no matter in the finite-size
scaling region or in the finite-time scaling region. Crossover between the two
regions is also demonstrated. We verify our theory using both the
one-dimensional transverse-field Ising model and the one-dimensional quantum
Potts model. Our results confirm that the Schmidt gap can be regarded as a
supplement to the local order parameter.
