SQL Server Filtering by DateTime column, when TIME portion is provided sometimes

In an SSRS report, the user searches based on start date and end date.

The challenge is, as I discovered recently, he sometimes, not always, provides the time component while searching.

Currently, the filter is done like this:

if @pEndDate is null  
  SET @pEndDate = getdate()  
SET @PEndDate = DateAdd(dd,1,@PEndDate) 

SELECT ........
FROM .....
WHERE ( Createdon >= @PStartDate AND Createdon < @PEndDate)

This is fine when he searches without time (example - @PStartDate = 2/23/2015 and @PEndDate = 2/24/2015)

How should I structure the query to deal with the time portion when he provides it? (example - @PStartDate = 2/23/2015 15:00 and @PEndDate = 2/24/2015 15:00)

If this is answered elsewhere, please point me to it. Thank you.