Oral is less risky than having anal or vaginal sex. The only STIs could have a risk for are gonorrhea, chlamydia, syphilis and genital hsv1 (if you don't already have hsv1 genitally or orally).
Syphilis is uncommon in most developed countries, and I would not worry about it unless a chancre develops, or if you have a regular partner that you're concerned about. Most people test positive by 6 weeks if they're infected.
You can test for gonorrhea and chlamydia at 5-7 days, but I wouldn't be overly concerned. You can forget about HSV if you don't get an outbreak.