i got a bfp 2day and im about 10dpo .. due 4 af on the 9th jan ...
i used first response if this helps u ....

and my friend tested bfore her af,,, and she got bfn ... she got a bfp when her period was late.. so yes u still could b pg
so i reckon it all depends on the individual....

hope this helps u
all the best
savina
xx