It depends on the day. I've heard about them selling out the first hour the box office opens. And I've also heard about someone getting one an hour before the show. There's ten of them. And they are really worth it. But get there early to play it safe.
I did get a student rush ticket about an hour before performance. But, it was in the balcony rather then front row. If they sell out front row they then go to sell balcony tickets at student rush price. I was lucky in that I just needed a single ticket for myself and that was all they had left. And, this was a saturday night too.
This was before they changed their student rush policy from being able to buy in advance to just the day of. Even though they are sold the day of I don't know if they sell balcony tickets when the front row tickets are sold out.
"If you try to shag my husband while I am still alive, I will shove the art of motorcycle maintenance up your rancid little Cu**. That's a good dear"
Tom Stoppard's Rock N Roll