Does this help:

Declare @Start DATETIME2,

@End DATETIME2 = DATEADD(ms,-3,CONVERT(DATETIME2, CONVERT(DATE, DATEADD(DD,-DATEPART(DD, GETDATE()-1),GETDATE()))))

SELECT @Start = CONVERT(DATETIME2, CONVERT(DATE, DATEADD(DD, -DATEPART(DD, @End)+1,@End)))

SELECT @Start, @End

Select CONVERT(VARCHAR(4),DATEPART(MM, start))+'/'+CONVERT(VARCHAR(4), DATEPART(DD, start)) AS [Date],

COUNT (DISTINCT Username) AS uniquelogon

from Miview

Where Activity = 'Logon'

and Start BETWEEN @Start AND @End

GROUP BY CONVERT(VARCHAR(4),DATEPART(MM, start))+'/'+CONVERT(VARCHAR(4), DATEPART(DD, start))