Looking at the cycle forecast of the indices over 7 years, Williams correctly predicted the Nasdaq peaking around March 15 followed by extended weakness (true), and a bottom around October 22. He calls the current decline to continue till around May 20. He also called the S&P peak around March 7 (he was slightly early). Another indicator if the Dow vs. bond prices, which indicates that the Dow will fall further.
He called Nvidia to peak on March 12, though it happened on March 8. He calls a bottom for May 13, followed by a brief relief rally. This is based on data of the Nasdaq's patterns stretching back 7 years of the "cycle forecast". So, sell not until mid-May, then you can buy back.