  We present a new approach to calculating time eigenvalues of the neutron
transport operator (also known as $\alpha$ eigenvalues) by extending the
dynamic mode decomposition (DMD) to allow for non-uniform time steps. The new
method, called variable dynamic mode decomposition (VDMD), is shown to be
accurate when computing eigenvalues for systems that were infeasible with DMD
due to a large separation in time scales (such as those that occur in delayed
supercritical systems). The $\alpha$ eigenvalues of an infinite medium neutron
transport problem with delayed neutrons and consequently having multiple, very
different relevant time scales are computed. Furthermore, VDMD is shown to be
of similar accuracy to the original DMD approach when computing eigenvalues in
other systems where the previously studied DMD approach can be used.
