SELECT  Snapshot.xId,  MAX(Snapshot.TimeStamp) AS Timestamp_Actual,
                dateadd(dd, datediff(dd,0, MAX(Snapshot.TimeStamp)), 0) AS TimestampRange_Start,
                dateadd(MI, 1439, dateadd(dd, datediff(dd,0, MAX(Snapshot.TimeStamp)), 0)) AS TimestampRange_End
                FROM Snapshot
                GROUP BY Snapshot.xId

SELECT  Snapshot.xId,  MAX(Snapshot.TimeStamp) AS Timestamp_Actual,
                dateadd(mm, datediff(mm,0, MAX(Snapshot.TimeStamp)), 0) AS TimestampRange_Start,
                dateadd(dd, 0, dateadd(mm, datediff(mm,0, MAX(Snapshot.TimeStamp)), 0)) AS TimestampRange_End
                FROM Snapshot
                GROUP BY Snapshot.xId

SELECT Snapshot.xId, MAX(Snapshot.TimeStamp) AS Timestamp_Actual
  FROM Snapshot
 GROUP BY Snapshot.xId
HAVING MAX(Snapshot.TimeStamp) >= dateadd(mm, datediff(mm, 0, getdate()), 0)
   AND MAX(Snapshot.TimeStamp) <  dateadd(mm, 1+datediff(mm, 0, getdate()), 0)