Hello, ARS is the first stage of an HIV infection, is the body’s reaction to the infection. Some HIV positive people, but not all of them, reported that around 20 days after their exposure they had fever, sore throat, rash and flu (not cold) like symptoms, all of those came together, or within a few days of difference and lasted for a few weeks. As you see, the same symptoms are present in many other illnesses and not everyone had them, so, we can’t rely on them to diagnose HIV.
About testing, third and fourth gen Elisa tests are among the most common ones nowadays, according to CDC, they are conclusive if taken 12 weeks after an exposure.
But you can take them before that, 3rd gen will give you an excellent indicator about your status around 8 - 10 weeks after exposure and 4th gen 4 - 6 weeks after exposure. A result taken in those time is very unlike to change, but only a doctor, based on your risk level and his experience could advice you to skip the confirmatory test after 12 weeks post exposure.