The practical limit is explained on my article on
$HTMLFileNameMaxLength, though it's not a page you'd otherwise rush to read!
It looks like TB still uses 'Classic' Mac max filename length limits. If you need longer, I'd mail in a feature request to move to OS X based limits.
For now, testing in v5.9.1, it looks like the maximum allowed filename length - with a '.txt' extension is 27, or 31 if you use no extension.
Don't forget, it's not all Tinderbox' fault, you could try addressing Scrivener's limitations at the other end. I'm less well placed to comment on the latter as I don't have/use the app. It is worth bearing in mind, as often here we go through complex changes/workarounds just because of the limitations of other apps. Of course, other apps developers are less flexible, but that doesn't sound the case with Scrivener.
If your notes are using $Text, or its first paragraph as the $Name,
consider moving the text back into $Text and using a shorter name. It might not be the process you originally intended but it might achieve the same end
Another approach, use TB Export as Text to export all the notes as one piece of text via a template that delimits each note's content with an easily searched for marker string, e.g. "##########". Then in Scrivener, after import use its equivalent of Explode (surely it has one?) to tease the single run of text back in to 123 notes.