If you are using SQL Server, this is typical. There is a way to force it all to use the Date only;
Under File/Report Options, set the "Convert Date-Time Field:" to "Date".
AND
Under File/Options, go to the Reporting tab and also set the "Convert Date-Time Field:" to "Date".
You may need to revise the existing fields, but it should all be Date format from then onwards.
If you do not do it this way, you may find that Dates are assumed to have 12:00 am (ie midnight starting that date) as the Datetime value. In date ranges, you will then need to use the tomorrow's date if you want today's data, for example.
It is helpful to show the date range used on the report in the report header or footer ("Report includes orders opened between Minimum(opendate) and Maximum(opendate)" for example. It doesn't show the range itself unless you have results for every date in the range, but should be close enough)