how to calcalate idle time

my requirement maxim idle time calculale my table structure(table one table name(tb_BusDetails) my field busid, IMEI,VehicleRegisterNo

second table Busid, LogDateTime

already i calating datetimeday d:H:r:s

select a.LogDateTime , CAST(DATEDIFF(DAY ,a.LogDateTime, GETDATE()) % 24/7 AS NVARCHAR(50)) + ':' +

 CAST(DATEDIFF(HOUR ,a.LogDateTime, GETDATE())  % 24  AS NVARCHAR(50)) + ':' +
 CAST(DATEDIFF(MINUTE, a.LogDateTime, GETDATE()) % 60 AS NVARCHAR(50)) + ':'+
   CAST(DATEDIFF(SECOND ,a.LogDateTime, GETDATE())%60 AS NVARCHAR(50))  as Duration 

  from tb_VTSData as a inner join tb_BusDetails as b on a.BusID=1 

plz any one help urgent