I am pretty sure my DS implanted at 11 or 12 DPO. I got BFNs at 10&11 DPO, a temp below the coverline at 12 DPO, then tested again and got + at 14 DPO.
I have a charting friend who regularly has 16+ day LPs. Even one that was 20 days once, and she wasn't pregnant. The fertility books all say 18 high temps = pregnant, but not for her.
Expat mama to my 7-year-old Halloween boy and my cheeky preschooler, who came before the midwife in January 2010... Gestating a new bean, debuting spring 2014!