How long does the passport renewal take?

I live in Quebec City - there's a US consulate here, but all there appointment slots are booked solid, so I'll have to renew my passport by mail. The State Department guidelines say the application must be mailed by Canada Post (aka snail mail...), and there's no estimate for how long the whole process will take.

I had some really bad experiences with cross-border letters: they'd take weeks to get here. :( If you've recently renewed your US passport, how long did the basic (non-expedited) process take you? (I'm not in a hurry to travel, but I'd like to have the whole thing done by January, ideally.)

Thanks in advance! :)