The production has not announced a closing date. It could be that the current block of tickets is on sale through March 26th, so NYTix is just stating that is the closing date (as the previous poster mentioned, they are not a very credible source).
That being said, while the production has gotten a temporary boost from Lea Michele, it's still a question of how long it will be able to sustain that sort of business, especially in the historically slow months immediately after the holiday season ends.