Personally, I don't really like the translation "information about A and B is insufficient to rule out implication". At least when I say "A implies B" I mean exactly "A => B". But maybe I hang out with too many mathematicians.
Other common translations you might be interested in are "A suffices for B" or "B is necessary for A". Though admittedly these particular words have a bit of a mathy tone, so no wonder they are so precisely tied to the definition of implication.
As far as your idea of "outside information" goes, I'm afraid it kind of breaks outside the bounds of sentential logic, which cannot deal with numbers in the manner you are attempting. However, that does not mean we cannot analyze it with logic. It should be simple to put your sentences into the logical "language" of Arithmetic and to prove more or less what you would expect: A is false (because John never leaves the office before 5), B is false (because it takes him 30 minutes to get home), and that "A => B" is true (by the definition of material implication, however vacuously).
Other common translations you might be interested in are "A suffices for B" or "B is necessary for A". Though admittedly these particular words have a bit of a mathy tone, so no wonder they are so precisely tied to the definition of implication.
As far as your idea of "outside information" goes, I'm afraid it kind of breaks outside the bounds of sentential logic, which cannot deal with numbers in the manner you are attempting. However, that does not mean we cannot analyze it with logic. It should be simple to put your sentences into the logical "language" of Arithmetic and to prove more or less what you would expect: A is false (because John never leaves the office before 5), B is false (because it takes him 30 minutes to get home), and that "A => B" is true (by the definition of material implication, however vacuously).