Heyyyyy!
Well it really depends, if you mean from the first stage i.e. producer auditions it can take ages! And, it's over two days.
Stage 1/first producer audition; it's the open audition, there's a lot of queuing due to the amount of people haha! You then sing to a producer in a booth thingy and get a straight yes or no. If you're gonna go dress warmly and take some food. I submitted an video so I didn't have to go to that.
Stage 2/second producer audition: You do a bit of queuing but it's nothing compared to the previous day and it's mainly indoors. You go into a holding room and kinda chill for a bit waiting for your name to be called, you then go into a room with some producers (there are loads of rooms, so waiting's not that bad) it's really nerve-racking, in my rooms loads of people were getting no's... luckily I got through, but that stage took from 12pm - 3.30/4.00pm
Stage 3/contracts/interviews and executive producer audition: Yeah that was cool, the interview is with one of the researchers, it isn't all that bad and they're really nice! You then sign a few contracts and fill in questionnaires and then you're taken for your final filmed audition; which you don't hear back from for another month. I eventually got out at 7.30.
I thought it was a really cool experience and I wouldn't be nervous, just be yourself and do your best; you can't do any more! If you're thinking of audition go for it! Just be prepared for a long day.
Any more questions fire away!