According to the ITIA website, “The players listed here have declared themselves retired from the sport and may not return to sanctioned events unless they have made themselves available for out-of-competition testing for at least six months prior to the event in question.”
This effectively rules Williams and fellow “evolvee” Roger Federer—who joined the ITIA list on September 26 after playing his final match at Laver Cup alongside Rafael Nadal—out of the 2023 Australian Open, the sport’s next Grand Slam event in January.
Andy Roddick ran headlong into this issue ahead of the 2014 US Open, when he attempted to enter the men’s doubles event with good friend Mardy Fish. At the time, the ITIA only required a three-month cooling period to enter competition, but the 2003 champion, who retired in 2012, made the decision too late.
In short, if Williams wanted to make a run at, say, the 2023 Wimbledon Championships, she would need to remove herself from the ITIA list by the end of the year at the latest.