I'm going to describe both the 3rd generation ELISA test and the 4th generation DUO test for you. The ELISA test looks for antibodies in your blood that your body develops in response to an
HIV infection. The window period is the point from first infection until the test can reliably detect antibodies in the blood. For the ELISA test this window period is 4 weeks to 3 months.
A 4th generation test like the one you took, also known as a DUO or Combo test, looks for both antibodies and P24 protein antigens. The P24 antigens can be detected within the first few weeks post-exposure, so this therefore shortens the window period for the test. Many HIV specialists consider this test conclusive at 6 weeks. This test is not necessarily "better" than the ELISA test, it can simply produce more accurate results earlier than the ELISA test. Your CMIA 4th generation test result is therefore conclusive at 6 weeks post-exposure.