Public Sub ConvertToTime()
    Dim wb As Workbook
    Dim cel As Range
    Dim rng As Range
    Dim intHours As Integer
    Dim intMinutes As Integer
    Dim avarItems As Variant
    
    Set wb = ThisWorkbook
    Set rng = wb.Worksheets("Лист1").Range("A1").CurrentRegion
    
    For Each cel In rng.Cells
        avarItems = Split(cel.Value, ".")
        
        If (avarItems( 0 ) \  60 ) >  1  Then
            intHours = avarItems( 0 ) \  60 
            intMinutes = avarItems( 0 ) Mod  60 
        Else
            intHours =  0 
            intMinutes = avarItems( 0 )
        End If
        
        cel.Offset( 0 ,  1 ).NumberFormat = "h:mm:ss"
        cel.Offset( 0 ,  1 ).Value = _
          TimeSerial(intHours, intMinutes, avarItems( 1 ))
    Next cel
End Sub

Public Sub ConvertToTime2()
    Dim wb As Workbook
    Dim cel As Range
    Dim rng As Range
    Dim lngHours As Long
    Dim lngSeconds As Long
    Dim avarItems As Variant
    
    Set wb = ThisWorkbook
    Set rng = wb.Worksheets("Лист1").Range("A1").CurrentRegion
    
    For Each cel In rng.Cells
        avarItems = Split(cel.Value, ".")
        
        lngSeconds = avarItems( 0 ) *  60  + avarItems( 1 )
               
        cel.Offset( 0 ,  1 ).NumberFormat = "h:mm:ss"
        cel.Offset( 0 ,  1 ).Value = Format(lngSeconds \  3600 , "00") & ":" & _
          Format((lngSeconds \  60 ) Mod  60 , "00") & ":" & _
          Format(lngSeconds Mod  60 , "00")
    Next cel
End Sub