I DCA TQQQ, but you have to know that in 2008, for example, had a 96% drawdown. The triple leverage can basically wipe out your entire equity, so you need a strong stomach.
I just do it in my play money account. Casual day trading wastes too much time that I could otherwise waste on HN, so I risk my money with TQQQ instead.
TQQQ indexes the Nasdaq 100, not remotely close to "the entire stock market".