I'm impressed also by your quite logical but sensitive approach to this whole thing. I think you are asking a lot of the right questions and trying to be fair & balanced about what the answers may be. Admirable !
The little 10 day test run was smart. All the theory in the world isn't worth the paper it's written on until it's tested. And you seem to have discovered what most experienced people probably would have expected.
In any active poly relationship, balancing time may be one of the biggest challenge in an otherwise wonderful setup. It's the one thing we can't control (the clock). And in order for it to not be a sore spot and cause problems - this is something EVERYONE has to understand and embrace. That fact that your SO seems to feel uncomfortable with her time being treated as a 'commodity' kinds of tells me she may have thought a little about that somewhere along the line, but never truly embraced it. Now she sees the truth of it and has to rethink what it means - because it's inescapable. There WILL be some sacrifices required by everyone. You seem to have a decent grasp of this - the other two may not ! But if handled properly the benefits outweigh the sacrifice.
It seems you also quickly identified the potential difficulty of having a mono minded person trying to live and cope in a full time 24/7 poly arrangement. It would take a special person ! It's a complete relearning process for anyone who has thought & lived mono all their lives. Because whether to adopt the label themselves (poly) or not is really quite immaterial. They WOULD be living a poly life. That's just the reality of it. Call themselves what they want - it doesn't matter. Living it requires developing the skill set - not just adopting (or rejecting) a new label
You two (SOBF) would have to become a lot closer than you are now for it to not turn into a soap opera.
So I think you are processing the whole thing very well. Experiment, test, observe, analyze findings and discuss honestly and openly accordingly.