It depends on your expected winrate ("edge") vs the player pool, and the standard deviation in your results. i.e. Having an expectation of 20bb/100 would mean you are likely to be winning even over a small sample, but an EV of 1bb/100 could mean you have to play hundreds of thousands of hands before you're certain of profiting. In addition, playing 200bb PLO, your results would be "swingier" than playing 10bb push/fold NLH.
Put some numbers into the variance simulator at
http://pokerdope.com/poker-variance-calculator/ and read the text underneath.