How late during the cycle can a fertilized egg implant?

Kasie • 23·Happily Married· Mama to Ellee Brynn Heller June 1st 2017❤
What's the DPO time frame that a fertilized egg can implant? I read somewhere up to 12 DPO. If that's true, then a BFP may not happen until 18-20 DPO? I wasn't sure if this was true or not....