I really hope this team here will give me an answer.
Window period for HIV depends on the kind of test you go for.
-If is a combo duo ag/ab it will be accurate 28 days after the encounter.
-If is a normal antibody test (finge-prick) it will be accurate 3 months after the exposure.
Regarding syphilis, 6 weeks is a good time to wait before testing. But if you get it negative, is good to re-test 3 months after the sexual exposure, as there are people that take longer to show a positive result.
All the best.
Meant to say at the end I have you ever heard of a neg RPR 4 months change at 6 months ?