Render value_template of the parameter using context.
        
        :param context: Processing context

def process(self, **context):
        """
        Render value_template of the parameter using context.
        
        :param context: Processing context
        """
        env = Environment(extensions=['jinja2_time.TimeExtension'])        
        value_template = env.from_string(self.value_template)
        return value_template.render(**context)