Set time portion of a datetime variable

Question

I am working on a query that will be an automated job. It needs to find all the transactions between 8 PM and 8 PM for the last day. I was thinking of doing something like

Answer 1

This will also work:

DECLARE @start_date datetime
DECLARE @end_date datetime

SET @start_date = LEFT(CONVERT(nvarchar, DATEADD(DAY, -2, GETDATE()), 120), 11) + N'20:00:00'
SET @end_date = @start_date + 1

select @start_date, @end_date

Although cyberkiwi's answer is very clever! =)