Can a embryo take up to three weeks to implant? what's the longest it's been known to take?

Please clarify?: A human embryo can implant 6-7 days after fertilization, and will produce detectable hCG (if the pregnancy proceeds normally) by about 10-11 days. This is 2-3 days before the expected period. An embryo cannot implant as late as 3 weeks after fertilization. I hope this helps, please submit again and clarify if you are asking a different question. Good wishes.