Ignoring the 1/32 chance that the wrong IV is inherited and it's still a 31, you have roughly a 1/24 chance of breeding your target larvitar. There's the 1/6 chance that the Destiny Knot will inherit all IVs but Special Attack, then the two 1/2 chances (1/4 total) that your baby won't inherit two relevant imperfect IVs from the Ditto parent. However, if somewhere along the way you get a female offspring with 4 31 IVs and replace Ditto with it, your chances shoot to 1/12, so be sure to substitute out Ditto if a better parent spawns along the way. Traditional breeding was the worst. I remember in gen 4, I spent maybe two weeks getting a near flawless Tauros. As for breeding more efficiently in the future, be sure to substitute out worse parents if better spawn, even if the other parent is a Ditto. Also be sure to use that hatching pass power as much as possible. You can always manage to find someone on #smogonwifi who has one for you to share between Hozu, Nexus, Lue, and me!