I don't get why you'd use Huton above 20s? It makes no sense in my head.
If you manage to get a Ration off at 21s, your Mudra's will be available again (without kassatsu of course) with 1s left on your Huton, where you should be reapplying it. Yes, that is technically making it fall off, but it's falling off as you're recasting it thus your GDC's nor AA's should be affected (unless you're unlucky and your AA is supposed to happen during that 0.5s downtime)