I personally have a tongue piercing and have had it for 3 years. I don't have the big silver ball though. Instead, to keep my parents from seeing it when I first got it, I used a flat flesh-colored stud thing (don't exactly know what it's called) so it wasn't obvious. I forgot to take it out for my committee interviews and it was not mentioned at all in my reviews or during my interview.
However, for my interview, I just took it out before my interview and after it was done, I went to the bathroom to put it back in (to prevent the hole from closing). No one said anything about it throughout the day.
I guess it all depends on how comfortable you are with it. If you're applying now, you may not have enough time to let it heal so that you can take it out. If you have to ask or are concerned about it, then I would just wait until you get that first acceptance letter.