6 week intervals would most likely suffice, and you can always schedule the next a little sooner if your horse is getting more much more than a 1/4 in nipped off. If it's less than that, 6 weeks should suffice.
Ahh, yes, they like to find the ONE spot that you'd like to have them avoid, eh? LOL Is he digging enough to wear out the toe between trims or is it just this one blowout that has you worried? Really, boots aren't practical for all day wear, just for exercise of short term therapy for founder/navicular. I'd patch up that last section of unmatted floor, or not worry, unless he's wearing out the hoof, which is unlikely.
Just out of curiostity, does his foot look ANYTHING like this? The first two are the same foot, before and after, the last is another horse. :