Hello @PeterWorrest, welcome to the Seller Community!
The Square Online Store wasn't built with mobile browsers in mind. So some themes display differently on mobile then others. For example if you're using the Roebling theme it will display a banner with the event date and time on a mobile browser. On the flip side if you're using the Atlas theme there will be no banner with the time and date.
If you want to stick with the theme that you're using, I recommend including the date and time of your event in the details section. The details should still be displayed on the mobile browser version.
