If you don’t believe in it, we recommend you for doing it and you will not be sinful for taking it off but it is best for you to keep it all the time just to be safe that your opinion might be wrong on the day of judgment. 

I am more convinced that niqab is a mere recommendation . So can I do niqab sometimes as it is recommended so as to earn more rewards. And can I remove it sometimes as I don’t think it’s fard and hence will not be sinning in sha Allah ?