Insert rows based on start/end values

Here is a code that should work. At least it does with the sample date you supplied. Also, look at attached file.

Option Explicit
Public User_no(10, 2) As Variant
Public User_Start As Integer
Public User_End As Integer

Public Sub test()
Dim U_ser As String, C_ell As Range, i As Integer, M_onth As Integer, D_ay As Integer
Dim First_row As Boolean, Current_hour As Integer, Last_row As Boolean, First_time As Boolean
'store Users values in array
Worksheets("Users").Select
i = 0
For Each C_ell In Range("A2", Cells(Rows.Count, 1).End(xlUp))
    User_no(i, 0) = C_ell
    User_no(i, 1) = C_ell.Offset(0, 1)
    User_no(i, 2) = C_ell.Offset(0, 2)
    i = i + 1
Next

'Scan whole sheet1 to insert rows where appropriate
Worksheets("Sheet1").Select
First_row = True
Last_row = False
First_time = True 'Variable only there to get through first row when hour equal start time
                  'otherwise you get an error because of the -1 offset
For Each C_ell In Range("A2", Cells(Rows.Count, 1).End(xlUp))
    'Assign value to variables
    U_ser = C_ell.Offset(0, 3)
    M_onth = C_ell.Offset(0, 4)
    D_ay = C_ell.Offset(0, 5)
    
    'check if NEXT row is a new entry (User, Month or day)
    If U_ser <> C_ell.Offset(1, 3) Or M_onth <> C_ell.Offset(1, 4) Or D_ay <> C_ell.Offset(1, 5) Then
        Last_row = True
    End If
        If First_row = True Then
            F_user (C_ell.Offset(0, 3)) 'Get start and end time for the user
        End If
        Current_hour = C_ell.Offset(0, 6) 'This is the hour of current row
        
        If First_row = True Then
            If Current_hour > User_Start And Current_hour <= User_End Then
                For i = User_Start To Current_hour - 1
                  Rows(C_ell.Row).Select
                  Selection.Insert Shift:=xlDown, CopyOrigin:=xlFormatFromLeftOrAbove
                  C_ell.Offset(-1, 3) = U_ser
                  C_ell.Offset(-1, 4) = C_ell.Offset(0, 4)
                  C_ell.Offset(-1, 5) = C_ell.Offset(0, 5)
                  C_ell.Offset(-1, 6) = i
                  C_ell.Offset(-1, 7) = 0
                Next i
                First_row = False
            ElseIf Current_hour = User_Start Then
              First_row = False
            End If
        End If
        
        If Last_row = True Then
            If Current_hour < User_End Then
                For i = User_End To Current_hour + 1 Step -1
                  Rows(C_ell.Row + 1).Select
                  Selection.Insert Shift:=xlDown, CopyOrigin:=xlFormatFromLeftOrAbove
                  C_ell.Offset(1, 3) = U_ser
                  C_ell.Offset(1, 4) = C_ell.Offset(0, 4)
                  C_ell.Offset(1, 5) = C_ell.Offset(0, 5)
                  C_ell.Offset(1, 6) = i
                  C_ell.Offset(1, 7) = 0
                Next i
                Last_row = False
            Else
                Last_row = False
                First_row = True
            End If
        ElseIf First_time = False Then
          If (Current_hour > C_ell.Offset(-1, 6) + 1) And Current_hour <= User_End Then
            For i = C_ell.Offset(-1, 6) + 1 To Current_hour - 1
                Rows(C_ell.Row).Select
                Selection.Insert Shift:=xlDown, CopyOrigin:=xlFormatFromLeftOrAbove
                C_ell.Offset(-1, 3) = U_ser
                C_ell.Offset(-1, 4) = C_ell.Offset(0, 4)
                C_ell.Offset(-1, 5) = C_ell.Offset(0, 5)
                C_ell.Offset(-1, 6) = i
                C_ell.Offset(-1, 7) = 0
            Next i
          End If
        End If
        First_time = False
Next
End Sub

Public Function F_user(User_to_F As String) As String
Dim I_1 As Long
For I_1 = 0 To UBound(User_no())
    If User_to_F = User_no(I_1, 0) Then
        User_Start = User_no(I_1, 1)
        User_End = User_no(I_1, 2)
        Exit For
    End If
Next I_1

End Function