There is no definite timeline for how long you should practice virtual trading before starting with the real thing. It is entirely dependent on your investment goals. If you are interested in long-term buy-and-hold investing, it is not necessary to indulge in the paper trade. You can simply go in for index funds, Robo advisors, target-date funds, and other long-term investment strategies.
But, if you are interested in options trading, day trading, and other advanced strategies, you can benefit from virtual trading. You should practice till you understand the investments you’re interested in completely and feel confident in your abilities to start trading with real money.