Unique timeline from the overlapping time stamp

Hi Anonymous 

Only use the Start Time and End Time, so the number is slightly different from the difference, 

M solution:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("zZPNqsIwEIVfRboWnEwyUbMT3blTXImLIkEL17a01ee3PyJmUivFe/VCFp1Twvkmc2a7DVY2T87Z3g5EMAxmafoT7cMiSuK6BhyBGiGgGAgykjxJQSWBATKgy8/1ObXZJcqTrL6/sGmYFScbF3U5P9o4DqPK6NBou+G/JsCvE8iPE+DLKagWCW8EYJBcAnQJsD+BPwXVIsk7gZy8SyAZgfLsiBNoQ/VghAFZHpdAugSyP4Hf8F8TKEbAYzc2NPGl6X0KguVAuQRVuVk+M6cX7fvmKJrklb3j2FuDXuaameuenUN3/pg5dj8737XuznXz97eeneUe0dt9LE1vu69Es4QP5uSaU3vqdlc=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Employee = _t, #"App Category" = _t, #"Start Time" = _t, #"End Time" = _t, Difference = _t, Supervisor = _t, Department = _t, Location = _t, #"Resolved by" = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Employee", type text}, {"App Category", type text}, {"Start Time", type datetime}, {"End Time", type datetime}, {"Difference", type time}, {"Supervisor", type text}, {"Department", type text}, {"Location", type text}, {"Resolved by", type text}}),
    #"Inserted Date" = Table.AddColumn(#"Changed Type", "Date", each DateTime.Date([Start Time]), type date),
    #"Sorted Rows" = Table.Sort(#"Inserted Date",{{"Start Time", Order.Ascending}}),
    #"Grouped Rows" = Table.Group(#"Sorted Rows", {"Employee", "Date"}, {{"allrows", each _, type table [Employee=nullable text, App Category=nullable text, Start Time=nullable datetime, End Time=nullable datetime, Difference=nullable time, Supervisor=nullable text, Department=nullable text, Location=nullable text, Resolved by=nullable text, Date=date]}}),
    #"Added Custom" = Table.AddColumn(#"Grouped Rows", "Custom", each [a=Table.AddIndexColumn([allrows],"Index",0,1),
b=Table.ExpandRecordColumn(
  Table.AddColumn(
   a,
    "MaxTime",
    (OT) =>
      Table.Max(
        Table.SelectColumns(
          Table.SelectRows(a, (IT) => IT[Index] <= OT[Index]),
          "End Time"
        ),
        "End Time"
      )
  ),
  "MaxTime",
  {"End Time"},
  {"MaxTime"}
),
c=Table.AddColumn(
  b,
  "Break",
  each [
    x = try b[Start Time]{[Index] + 1} - [MaxTime] otherwise 0,
    y = Duration.From( if Number.From(x) > 0 then x else 0)
  ][y]
)][c]),
    #"Added Custom1" = Table.AddColumn(#"Added Custom", "Downtime", each List.Max([Custom][End Time])- List.Min([Custom][Start Time])-Duration.From( List.Sum([Custom][Break]))),
    #"Removed Columns" = Table.RemoveColumns(#"Added Custom1",{"allrows", "Custom"})
in
    #"Removed Columns"

DAX solution:

calculated column

Break = 
VAR CurEmployee = overlap[Employee]
VAR CurDate = overlap[Date]
VAR CurrentTime = overlap[Start Time]
VAR PreviousMax =
    CALCULATE (
        MAX ( overlap[End Time] ),
        FILTER (overlap, overlap[Start Time] < CurrentTime && overlap[Date]=CurDate&&overlap[Employee]=CurEmployee)
    )
VAR MaxTime =
    COALESCE( PreviousMax, [End Time])
VAR Break =
    IFERROR(DATEDIFF(MaxTime,CurrentTime,SECOND),0)
RETURN
    IF(Break<0,0,Break)

measure 

Downtime = 
VAR Totalsecs = DATEDIFF(MIN(overlap[Start Time]),MAX(overlap[End Time]),SECOND) - SUM(overlap[Break])
VAR Hours = INT(Totalsecs/3600)
VAR Mins = INT((Totalsecs-Hours*3600)/60)
VAR Secs = Totalsecs-Hours*3600-Mins*60
RETURN
Hours&":"&Mins&":"&Secs