I believe it should be "Middle(Source_TC_in;3;2)" to extract the third and fourth numbers. Your time code is short two numbers and doesn't conform to SMPTE standard, which is (2 digits each) hour:minute:second:frame . Unless the hour is assumed or auto-entered I suppose . . .
You are correct. It became complicated because I wanted to create a duration field. Which meant that I had split out the Frames because I was trying to figure out a calculation to allow me to figure out the duration of shots.
If you are dealing with 6 digits only, you could use =
Time ( Div ( TC ; 10^4 ) ; Div ( Mod ( TC ; 10^4 ) ; 10^2 ) ; Mod ( TC ; 10^2 ) )
This way they don't need to enter the leading zeros.
And, I should add, they can edit the entry without getting an error if they don't remove the separators first.