CREATE PROCEDURE dbo.MySingleDaySearch
        @inputDate datetime
AS

DECLARE @startDate datetime;
DECLARE @endDate datetime;

SET @startDate = dateadd(day, datediff(day, 0, @inputDate), 0);  -- remove time portion
SET @endDate = dateadd(day, 1, @startDate);  -- set the end date to tomorrow

SELECT ...
   FROM dbo.MyTable t
  WHERE t.MyDateColumn >= @startDate
     AND t.MyDateColumn < @endDate;
GO