I started playing with this a little bit yesterday. I didn’t need to do a formula in the sheet to format the date. Instead I just set the formatting in the date column and created a template column to “lock in” the date that was formatted within Glide. The template is what I use for grouping. I think the underlying issue is that the grouping will still actually use the underlying timestamp value, so if the days match, but the times don’t exactly match, then they are grouped separately. I did however still need a formula in the sheet to duplicate the date column, so I could have a separate column that I can format in Glide to only displays the time.
Here’s what I have for a quick test so far.
