They will be distinct if both dates are the same for 2 or more records. So your records would show grouped together if you had values like so:
Record 1:
01/04/2019 09:00:00
01/04/2019 17:00:00
Record 2:
01/04/2019 09:00:00
01/04/2019 17:00:00
If even the time is off by 1/10 of a second they are not considered the same values so you won't get unique values. If you're looking to get unique dates you should exclude the time in your query and cast it to a short date value.