Carla

From my past attempts - I have pretty much learnt that if a HPT says neg around 12 dpo then it is usually (although not always) going to be neg.
All the research I have done over past 5 months suggests that implantation occurs between day 6-12. Even if it was late - say day 12 which is not that common then you should get enough hcg by 14dpo however, again not always.
I am in a similar boat.

Today is day 10 post transfer for me - the day AF always comes unless there has been some implanting action of some kind, although I did a HPT yesterday and it was BFN so I suspect AF will still arrive today/ tonight sometime or if it doesn't that the little embbie tried to implant but hasn't made it. Who knows. It will be what it will be.
I have brought blood test forward to sunday instead of Tues but AF will probably arrive before then. I feel like it is on its way - but the only other time it didn't come on day 10 post transfer so (12 DPO) which is my luteal phase was when it implanted but the hcg was too low for it to be viable and AF ended up coming later.
Good luck to you anyway - I read all the time about people getting BFP;s late and like at 17dpo etc etc - I just know my body and pretty much know that yesterdays HPT will be accurate if its neg
Hope that doesnt upset you - just trying to be honest given my experiences