Convert float to hours and minutes in this script

I would like to the diff(float) field to convert to hours and minutes. Am relatively new and don't know how to incorporate this into the below:

SELECT UserId, WorkDate, FirstIn, LunchOut, LunchIn, FinalOut, '07:00' As Roster,
     CONVERT(varchar(5), DATEADD(MINUTE, DATEDIFF(MINUTE, FirstIn, FinalOut) - 
         ISNULL(DATEDIFF(MINUTE,LunchOut, LunchIn), 0), 0), 8) AS Time_Worked,
         CONVERT(float(5), DATEADD(MINUTE, DATEDIFF(MINUTE, FirstIn, FinalOut) - 
         ISNULL(DATEDIFF(MINUTE,LunchOut, LunchIn), 0), 0), 8) AS DIFF
 FROM (
     SELECT 
         UserId, CAST(DATEADD(DAY, DATEDIFF(DAY, 0, [when_adjusted]), 0) AS date) AS WorkDate,
         ---MAX(CASE WHEN INOUT = 2 THEN '00:50' END) AS LunchFlex,
         MIN(CASE WHEN INOUT = 0 THEN [when_adjusted] END) AS FirstIn,
         MAX(CASE WHEN INOUT = 2 THEN [when_adjusted] END) AS LunchOut,
         MAX(CASE WHEN INOUT = 3 THEN [when_adjusted] END) AS LunchIn,
         MAX(CASE WHEN INOUT = 1 THEN [when_adjusted] END) AS FinalOut
     FROM [Safescan].[dbo].[attendant]
     CROSS APPLY (
         SELECT 
             CASE WHEN DATEPART(HOUR, [WHEN]) = 3 THEN DATEADD(MINUTE, CEILING(DATEDIFF(MINUTE, 0, [WHEN]) / 15.0) * 15, 0)
                  WHEN DATEPART(HOUR, [WHEN]) = 2 THEN DATEADD(MINUTE, FLOOR(DATEDIFF(MINUTE, 0, [WHEN]) / 15.0) * 15, 0)
                  ELSE [WHEN]
                 END AS when_adjusted
     ) AS adjust_when
     GROUP BY USERID, DATEADD(DAY, DATEDIFF(DAY, 0, [when_adjusted]), 0)
 ) AS derived
 ORDER BY WorkDate

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