The usual rule in Bucks is that you have 14 days to return the appeal form (14 days from the date of issue, that is). So, if your child is attending a Bucks school, I would expect the headteacher to issue the form at a meeting with you - and you would then have 14 days to return it. If there is a good reason for returning the form late, I think the appeals office would not be unsympathetic - but ask nicely.
Hearings usually take place from the very beginning of January until mid-February. To answer a question that comes up every year, it makes no difference whatsoever to the outcome of your appeal if you are heard first or last!
Panels take no account of individual schools at a selection appeal, or of the overall number of places that might be available.
Please post any appeal questions in the Appeals forum, but do remember to specify "Bucks" (as the forum deals with all parts of the country).
If you mention the score achieved, please say what the other score was as well. (120+119 makes for a stronger case than 120+110.) Every year someone will say "But it's not fair - if my child had scored 121, the lower score would be ignored." The answer, of course, is that we have moved on from the admission arrangements to an appeal, and that at an appeal the panel is entitled to consider all the available evidence. SATs predictions, headteacher recommendation, CAT scores, extenuating circumstances etc. are not part of the admission arrangements either!
It's always a help to have a username - too many "Guests" can be confusing.
Good luck to everyone