I always plan to arrive 20-30 minutes ahead of time, but usually a couple of times a year there is such a huge delay that even the extra padded time doesn't help.
Intending to arrive 20 minutes before curtain is not "extra padded time"; that's when you should arrive. Plan to arrive an hour and 20 minutes before curtain, and grab a bite first. And if you find the MTA to be so catastrophically unreliable, take a cab or an Uber.
