Technically, the question as worded and the answer match, but there was a given solution which contradicts the question by being worded incorrectly. "the solution should be..." should be...

Assuming you are using a view or procedure, you could also use something like the following:

declare @StartDate datetime

declare @StopDate datetime

set @StartDate = convert(char(10),Getdate()-1, 121)

--returns yesterday's date with time stamp = 00:00:00

set @StopDate =...