When to test??

So say he came in me only a day or two before my period was due (I know it’s only a very low possibility) and it did by some miracle get me pregnant would it take longer to get a positive? My period has been late for a week now and I’ve been feeling off but tested negative. I know there’s a good chance there’s some other explanation but since we had sex so close to when my period was due would I have to wait longer after my missed period to be able to test? Hope this makes sense, sorry it’s hard to explain.