Modify Query to Allow Drift in Timestamp

I use the query below to return data from a datalogger table, logging values every 15mins. The query should join the columns based on TLInstance and return in Rows where the Timestamp is the same.

The problem I have is sometimes the Timestamp can be 1-2secs different, so I need to add a tolerance into the query to allow for this slight difference.

Can anyone help out in adding this tolerance. I'm thinking it may be better to ignore the timestamp from all other Columns, and only return Timestamp from A_Value, and assume all other data will fit into that Timestamp.

select * from
(
  SELECT [Timestamp], data 
         , case when tlinstance = @TLInstance1 then 'A_Value' 
                when tlinstance = @TLInstance2 then 'B_Value'
                when tlinstance = @TLInstance3 then 'C_Value'
                when tlinstance = @TLInstance4 then 'D_Value'
                when tlinstance = @TLInstance5 then 'E_Value'
                else 'F_Value' end as Value_Code
  FROM TLData
  WHERE TLInstance in (@TLInstance1,@TLInstance2,@TLInstance3,@TLInstance4,@TLInstance5,@TLInstance6) and isnumeric(data)=1 and Type=0 and (timestamp>@SDate and Timestamp < @EDate)
  UNION ALL
  SELECT [Timestamp], tl.name 
         , case when tl.tlinstance = @TLInstance1 then 'A_Name' 
                when tl.tlinstance = @TLInstance2 then 'B_Name'
                when tl.tlinstance = @TLInstance3 then 'C_Name'
                when tl.tlinstance = @TLInstance4 then 'D_Name'
                when tl.tlinstance = @TLInstance5 then 'E_Name'
                else 'F_Name' end as Value_Code
  FROM TLData
  INNER JOIN TL on TLDATA.TLINSTANCE = TL.TLINSTANCE
  WHERE tldata.TLInstance in (@TLInstance1,@TLInstance2,@TLInstance3,@TLInstance4,@TLInstance5,@TLInstance6) and isnumeric(data)=1 and Type=0 and (timestamp>@SDate and Timestamp < @EDate)

) srce
PIVOT
( max(data) for Value_Code in ([A_Value],[A_Name],[B_Value],[B_Name],[C_Value],[C_Name],[D_Value],[D_Name],[E_Value],[E_Name],[F_Value],[F_Name])) pvt

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