No worries my young friend. I did not went for the IPPT test
prior to enlistment and they threw me into the PTP batch (extra two
months). But I think on the second or third week of the training
you will get to clear an IPPT test. Those who pass can get to
disrupt from the two months training and await the actual BMT
training.
I think after the first test there will be subsequent tests for you
to try and pass. And you can still get to go home after you pass
but obviously you dun get to spend as much time as the first batch
of disruptees. I dunno if this is still the same now. But do try
hard to do your best during training, you will be surprised how
much you can improve within a short one or two weeks.
I was the first batch of disruptees in my Company, there were only
30 plus disruptees for the first batch. It was quite a proud moment
as the passing rate was low and the sergeants asked us to write
messages of encouragements to fellow trainees. They had the
messages pasted on the notice board of the company line. And damn,
I was really happy to go home and relax for more than a month
before the actual BMT.
I really ran my hearts out for the 2.4km (I am quite a big guy, so
that was my biggest problem). I remembered passing out at the
finishing line, and had the medic attending to me, it did not help
that I was running a fever prior to the test. I came in 12.04
seconds btw. Not great, but enough. 
Those were the days. Have fun man.
