Thinking about the whole 8 hour limit before taking damage from unburnt metals (esp from pewter burn, mentioned in the pewter problems thread) I wanted to suggest a solution - just don't sweat the exact timing. To my mind "8 hours" is meant to stand basically in for "a long time, but not forever."
Ie - it is long enough that you could walk around for a good long while without problems...in fact it would allow Zane to swallow some metals before going to sleep and still have time to burn them off upon waking.
If you really think about it biologically though, it doesn't really make sense, does it? Food (and by extension, metals) takes 24-48 hours to be digested, but once eaten, stays in the stomach for only a few hours (no longer than the time between lunch and dinner, typically), then moves on to the small intestine. Now, assuming that metals for whatever reason (maybe the alcohol in the vial? maybe just because?) aren't digested by the stomach, that still leaves four or so hours before it moves on to the small intestine... So really metal would start to poison you far sooner, and in reality it would be the small amounts building up over time that would cause the problems...
My whole point though, is that the eight hour rule isn't based strictly on biology, but more on story needs, right? So basically, one should feel free to bend this rule around what feels right.
At least, that's my thought on the topic...