Update GSSHA simulation start time

def _update_simulation_start(self, simulation_start):
        """
        Update GSSHA simulation start time
        """
        self.simulation_start = simulation_start
        if self.simulation_duration is not None and self.simulation_start is not None:
            self.simulation_end = self.simulation_start + self.simulation_duration
        self._update_simulation_start_cards()