Exposure to COVID-19 - isolating at home

Hello. I met my friend 2 days ago on Sunday. Yesterday evening at work, he told me his younger sister has tested positive for COVID-19 at his home. He said he was feeling symptoms for a week.

As a precaution, I am self-isolating and working from home. Today is Tuesday, and Thankfully, I am not feeling any symptoms. I went to a local blood lab and got myself a COVID-19 antibody test done.

My question is, if God Forbid I am infected, how long does it take for the symptoms to show ? And also, does the antibody test show up negative if you get tested the very 2 days after exposure ?