You can accomplish this by adding another column that holds the date alone.
New column’s formula will be:
=DateTimeTruncate(dateStart,"days")
Full details on that truncate function here.
(Interestingly, it doesn’t matter whether this new column’s format is “Date” or “Date and Time”. I thought setting the column to date and just making the formula =dateStart would do the trick, but the event times get preserved deep inside somewhere).
If you’re not in Pacific time zone, this won’t work. You’ll need to adjust for your timezone so that you’re getting the events to land on 12:00:00 AM. If you were in Central time zone, your new column’s formula would instead be:
=DateTimeTruncate(dateStart,"days")-hours(2)
Drawback: you can’t drag and drop your events in calendar view using this approach.