You get 18 months to pass all the exams before the 24 month flying clock starts ticking.
If you do them too quickly and then have a problem in your life which stops you flying for a bit you'll have to resit the previous passed exams when they get to +18 months old.
My instructor is also an examiner and warned me about this when I knocked off 4 exams in 7 weeks - he basically told me to slow down - just in case of unforeseen future problems!!