Shortcode singular “minute” not displaying

I’ve inserted <?php echo do_shortcode(‘[rt_reading_time label=”Reading time:” postfix=”minutes”]’); ?> into the postinfo.php file in my child theme. Anything 2 minutes and longer displays “X minutes” but anything in the 1 minute length displays only “1”.

Examples at https://www.thepulp.net/yellowedperils/.

Any suggestions for displaying “minute” after the “1”?

Thanks in advance!