Why would patients that completed the trial enroll in another trial and risk being in the placebo group when they are already on the therapy for how many years?
12 week treatment of each patient, if that's what you wanted.
I'll add to RubyRed's excellent point, that the trial would be disqualified on the ground that the subjects, having been on blarcamesine previously, are not appropriate since the prior treatment might be affecting the things being measured.
Recruiting will take the longest amount of time. I would expect the trial size to be larger and probably a bit longer. Both of those changes would mitigate against a strong placebo effect.