I found a UDF function to get me the difference between two time codes. I now need a UDF to Sum the time keeping the frames at the end. Below is the VBA for the function I am using to get the duration between two times:

Function frameDur(fEnd As String, fStart As String) As String
Dim ofEnd As Single, ofStart As Single, e1 As Single, e2 As Single
Dim Ans As String, AllAns As String, T2 As String

Const AddTim = 0.0000115741

Const DivTim = 2592000

ofStart = Format(Left(fStart, 8), "General Number")
e1 = Right(fStart, 2) / DivTim
ofEnd = Format(Left(fEnd, 8), "General Number")
e2 = Right(fEnd, 2) / DivTim

If e1 > e2 Then
ofStart = ofStart + AddTim
End If

Ans = Format((ofEnd) - (ofStart), "hh:mm:ss")
AllAns = Round(((ofEnd + e2) - (ofStart + e1)) * DivTim) / 30
T2 = Round((AllAns - 1 * Int(AllAns / 1)) * 30)

If T2 < 10 Then T2 = "0" & T2
frameDur = Ans & ":" & T2

End Function

I now need to add the total duration. I would like a UDF for it.

result should end up like this:

00:06:53:29
00:06:28:07

Total: 00:13:21:01

Any help is greatly appreciated!