I am not sure what you mean by different trading strategies? That different trading strategies can take different time to learn or the more strategies you learn, the more time you need?
I agree about the mentor though. A mentor can make you or break you. The person who taught me taught me to have an open mind about everything, to experiment, to not be afraid to try new things, but it took her forever to free herself from the bias her own mentor instilled in her, since he only accepted the Elliot Wave Theory and nothing else.