All set: thought I'd share this for anyone who runs into the same issue.
At the beginning of the call flow, insert an Override. In the results for Override section, result: from call flow, I entered the 'weekly schedule'. result: disabled, I entered 'voicemail'. Works great now. The call went thru the call flow the first time via the AA call flow, was transferred to the extension (which rang 5 times, then call forward no answered back to the mailbox call flow, but this time it didn't come from the AA call flow, so the Override disabled sent it to Voicemail.