You might have to wait years. Even if the market goes down sharply, how do you know when the bottom is in?
In 2008, I was all in cash, fearing a big market correction. What I did when the market started selling off in earnest, was to gradually put money into a stock market index (although not leveraged) as the market fell, so that by March 2009 I was 100% in stocks. I suffered a small loss up till then, but a huge gain in the rest of 2009 and 2010, at which point I pulled some money out of stocks and into other investments.