Date field with time. Is there a way to not show the time until you fill it in manually?

So we’re tracking our incoming shipments. Some of them have a ETA with both date and time and some with only date. If i include a time in the date field it automatically sets the time to 00:00. Is there a way to make the time blank until you fill it in manually since it would be misleading to have shipments with no hourly ETA to be 00:00.