Just got my GASIL for March 2003 and in the GA Feedback thing is a great screed about this from the CAA FCL (it's on page2).
To paraphrase:
It's not a test, the AIC is only advice and can be completely ignored, although some operators have taken it to be gospel, and a revised AIC is intended to be issued and incorporated into LASORS. The instructor is quite at liberty to not sign if he thinks you are unsafe. An hour is an hour is an hour.