I had implantation bleeding ( slight bleed and pink in colour ) around the 14th October with period due 25th. I new I was pregnant and took that may home tests and each one came back negative. I took one on the 24th negative. I took one on the morning of the 25th ( day period due ) and POSITIVE. So within 12 hrs is went from negative to positive. Previous 3 pregnancies though I never tested positive too until 14 days after by due period. So everyone and every pregnancies is different. All the best