How long does one wait till it’s best to get an STD check?

Okay, so here’s the thing. I like sex, I don’t like relationships. For whatever reason I just don’t like people romantically. So, anyways, I have this friend, her and I are really close friends. One day she asked if I’d ever be interested in a threesome with her and her guy. Told her yeah, why not. So long story short, I’ve slept with them both on more than one occasion. Thing is, this recent time, no condom was involved. This was a slight on my part. I could’ve just declined instead of continuing but eh. Bad decisions happen sometimes. I’d already gotten up and taken a plan b the following morning just to be safe as far as pregnancy goes since I knew he came. But, the reason for this post is just, when can I go get tested? I’d like to do it ASAP to just be safe but idk if it’s too early or should I wait a couple days and then get tested?

I’m usually very proactive with these things but for some reason this info is slipping my mind. I feel like some unknowing teen, again. I usually never have this issue because I’ve always had a regular GYN. But this year I don’t and so seeing someone has been the worst headache ever.