Syphilis sores show up at the point of infection.
If you must test, it will be conclusive at 6 weeks. If you think this is syphilis, see a doctor now, though.
I see you've had a lot of questions for a long time regarding sex and stds/hiv. So, you already know what the risks are for HIV. Unprotected vaginal or anal sex or sharing IV drugs. You had protected sex, so therefore, had ZERO risk for HIV transmission. The sore has absolutely zero to do with that. And with regards to std's, some can come from skin to skin contact, however, you used a condom. Unless you think you got some sort of std on your abdomen which is pretty unlikely, this is also likely not the case. There is a small possibility it is a herpes outbreak as technically that can happen anywhere on the body. A rash from syphilis is usually related to latent phase and not from this encounter. So, it might be an ingrown hair, pimple, etc. nothing at all related to the sexual encounter. I would not be worried.