AIDS educators in the U.S. (I am a volunteer educator) maintain that while the window period is officially 13 weeks, a negative ELISA test at six weeks is an excellent indicator that you are fine.
The only people who take longer than 13 weeks to seroconvert (in other words, produce antibodies to the virus, which is what an ELISA HIV test looks for) are people with severely compromised immune systems, such as those with Hep C, or those receiving chemotherapy, etc.
If you look at the Web, you'll find things that say the window is six months. That's severely outdated. Modern tests have sharply reduced the window period.
That being said, your odds of being infected through sex with a sex worker while wearing a latex condom are basically nil. Even if the condom ruptures, it protects you during the time it is intact. HIV cannot penetrate skin; thus, the only real risk during condom failure is through the urethra, which is pretty hard to accomplish. During heterosexual intercourse, the risk to the woman is far greater than the risk to the man.
So, basically, I'm agreeing with cancowboy. And I will respectfully disagree with HN about the risk of receiving oral. The American CDC does not have a single confirmed case of a person being infected through receiving fellatio (but there is a risk to the woman, especially if she swallows.)
Hope this helps.
bumfie