Implantation bleeding

Alisha • Married 6.7.2014❤️baby #1 born 6.2015❤️👼🏻baby #2 born 4.2018 at 21 weeks👼🏻❤️baby #3 born 3.2019❤️baby #4 due 10.2021❤️
If you had this happen how many days before expected AF did you get it? Is it like a one time thing? Or happens over a day? I just want to know any details so I can compare what's going on with me! :)