The delta-perturbation that can be applied by making use of the TDDeltaStrength variable, can be applied at the time given by this variable. Usually, this time is zero, since one wants to apply the delta pertubation or "kick" at a system at equilibrium, and no other time-dependent external potential is used. However, one may want to apply a kick on top of a laser field, for example.
hamiltonian/kick.F90 : 156
call parse_variable(namespace, 'TDDeltaKickTime', M_ZERO, kick%time, units_inp%time)