There's not a lot of information out there, it's a lot of best-guessing and extrapolating from the small amount of data. Personally, my best guess now is 12 months. Andy Cutler is one of the best guys on mercury toxicity and a good resource on how our bodies start dumping mercury after we get our amalgams removed. I used to think it was only mercury toxic people who had this dumping phase, it's the time period from 3-6 months after the amalgams come out when a big shift occurs in the body and circulating metals significantly increase. Mercury toxic peoples' symptoms get worse during this time period, mine followed this pattern as well. The weird thing was that my husband, who detoxifies very well and definitely does not have mercury toxicity issues, and only got his amalgams replaced with composite on general principle, experienced the same thing (I think we saw the effects because he's very rundown in other ways). I did not expect this. So I really think being pregnant in the time period 3-9 mos post-amalgam removal is risky. The limited data I've seen says that around 9 mos out, the level of circulating toxins is comparable to before the amalgams were removed, and so then to give yourself 3 months of good levels before TTC, that's how I came up with 12 mos. But there's a lot of best-guessing mixed in there, and I wish Cutler had more data--I don't know anyone who has more data than he does, but it's still not a well-researched area.
But I really hope someone knows of a dentist who is good with the safe amalgam removal protocols! There are two mercury free dentists in the Houston area that advertise as such, but I found both to have very high pricing and I didn't choose them. I'd love to find someone reasonable locally, just to know them, and hey, maybe I can get my teeth cleaned!