It takes a microsecond [probably less]once a molecule of T gets places in an aromatase enzyme reaction site. The process is continuous. Consider TRT with EOD injections where T levels are constant.
As a T injection is absorbed, T levels increase, so T-->E2 increases. Your serum levels of E2 are the result of T-->E2 production rates and E2 clearance rates, primarily in the liver. As your T levels drop after an injection, your T:E ratio takes a hit from both sides. An AI reduces the T-->E2 production rate.
Some gear messes with the liver and E2 levels can get high. Increased AST/ALT in lab work is also a result of that.