If you have high IQ, interest in academics and have decent test taking skills, you don’t have to spend too much time on standardized testing, if you aren’t then your chances of scoring high enough on PSAT to make NMSF are very low, no matter how much time you dedicate. That’s what I’ve observed in kids around us, most kids hit a block at commended, no matter how many hours they spend at prep centers and how many flash cards mommy make them do every day.
Average kids should focus on SAT or even better at ACT, which is easier to score at. This is where hard work can help you improve.