To hide the cautionary time sig, you either need to use another Flow, or a hidden Coda. Personally I usually go for the Coda, but you may have to then set the default gap for a Coda to 0. If you search there are a ton of threads on this, and this functionality has been requested a bazillion times, but we are still stuck with workarounds. (I have to deal with this all the time with educational handouts, and personally find hidden Codas faster, but it would be great to be able to simply hide the cautionary like we can in other programs.)