How many days after conception can you take a first response 6 days sooner test?

I am specifically wondering how many days after you’ve had sex. I wasn’t tracking my period before I had sex so I don’t know when my period is suppose to come. If it helps my period definitely ended a few days to a week before I had sex and it’s been 12 days since I had sex. Can I take a test after 12/13 days?