I have not really understood from what you want to build your TOC but please do not build up fake Disc ID based on ripped files or something like that.
You will get inaccurate and/or rounded values.
We base our trust on Disc ID, they come from CD and have milliseconds.
If you do not have disc or trustworthy rip log, just set track times in the release editor, there is no need to add a fake CD TOC anyway, is it?
Even from rip logs, I am not sure there are no problems if you have not first scanned for track gaps, etc.