<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def pre_save(self, model_instance, add):
 """ Converts the value being saved based on `populate_from` and `time_override` """

        # pylint: disable=newstyle
        # Retrieve the currently entered datetime
        value = super(
            LinkedTZDateTimeField,
            self
        ).pre_save(
            model_instance=model_instance,
            add=add
        )

        # Convert the value to the correct time/timezone
        value = self._convert_value(
            value=value,
            model_instance=model_instance,
            add=add
        )

        setattr(model_instance, self.attname, value)

        return value