From Stretford Site I have answered one bit of my own question - the results for the alternative date will not be available until AFTER the 31st Oct Deadline for Preference Form.
I suppose one could argue discrimination on religious grounds if one really feels that one's child cannot take the test on the main date, but the practical implication is that one will be putting one or two schools on the CAF before knowing whether s/he qualifies for consideration for a place. If you have enough spaces on your LEA's form, you may not feel that this is a particular problem; a: it is just going back to the pre-Admissions Code situation and b: if you would instigate a 'non-qualification' appeal anyway should the worst happen, then you need to have applied to and been turned down by the school to be able to do this.
That being said, most areas do manage to fit in a reserve date in time to give results before 31st October. Does this school explain why they cannot?