How to keep Standby GTM up to date with zone transfers from Primary Masters

I hsve GTM servers config'ed as Master Slaves to Microsoft AD DNS servers, and they do zone transfers just fine. I want NOTIFY requests from the primary masters to update both F5's in an HA pair. I can get the Active unit to receive the notify and subsequently request a zone transfer, but the Standby unit has a stale record until the next refresh cycle timeout. I'd like to increase our refresh time to hours or maybe a day, but don't want the Standby GTM to be stale that long.

The notifies come into a VIP that does a SNAT back to the Master and forwards the request on to the GTM UDP Listener. That listener is only active on the ACTIVE GTM at any given time. Any recommendations for how to keep the Standby GTM up to date (mirror the Notify over to it, so that the Standby unit can request the zone transfer via IXFR, too). Or am I worried for nothing, that in the event of a GTM failover the zones will be refreshed anyway? I'm running version 12.1.2.