Jimmy,
Limits in JAR-world are only ever recommendations, the examiner is always able to use his discretion, e.g. if it happens to be a particularly bumpy day. (There are exceptions to this - minima for an instrument approach, for example, are always absolute - but none that apply to the CPL as far as I know.)
I can't remember the exact recommended maximum deviations - someone like Keygrip may be able to help you with the exact details. From memory (so they may be wrong), it's +/- 100' altitude, +/- 2 mins to arrive overhead or within a set distance (3nm?) of your destination, +/- 10kts on all airspeeds. I may have that completely wrong, though.
One thing which the examiner will make clear (well, Keygrip made it clear to me, I don't know if all examiners are the same) is that discretion can work both ways. For example: +/- 100' on altitude. If you notice the altitude is 110' higher than it should be, and immediately comment on it, and smoothly apply a positive correction, you won't fail. On the other hand, if you fly the whole of your navigation leg 90' above the altitude you planned, you will fail. So the message, really, is not to get too fixed on the details, but just fly as accurately as you can.
Once again, I refer you to my CPL Diary thread, because at the end of the thread Keygrip made a couple of excellent posts, including a complete transcript of a typical pre-flight brief from examiner to candidate for the test, and this will probably include most, if not all, of the requirements for the test.
FFF
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