I was being dumb. I thought I would have to add a whole new bit just to get the failed Bdu messages to use a timer but I don't. I can just simply give it a different value (2 instead of 1)

Thus when Bdu fails to dispatch subs to your position the message will be on the same timer used by when they do dispatch subs to your position (meaning it could take up to 1 hour to receive this message)