20 min, usually, tops, from near-frozen if the mass is thin. Normally I toss a bag into boiling water, cover the pot then shut the heat off. If he's doing them all at once in the same pot then I'd suggest leaving the heat going and covering the pot and leaving it alone for several minutes till the water returns to a good simmer (180). Then the heat can be lowered to a gentle simmer or simply shut off, left covered. The packs should be hot in less than 10 from there.