Well, of course, the other alternative to Mark's theory 'With one day's notice, I will be guaranteed to see that actor at the casting' is 'With one day's notice, I will be guaranteed NOT to see that actor at the casting' (i.e. because they have a clash with something else that you have not given them enough time to rearrange around, are in a different part of the country or, wonder of wonders, actually out on ANOTHER JOB!) - but then, with commercials especially, it has to be tacitly accepted that our actual attendance really *is* ten-a-penny, whether we turn up or not is of minor concern, and there is rarely any leeway on rearranging the casting for a different slot in the same day, let alone for another day. I still feel Guy's point has merit, however, inasmuch as it seems that the lead-time being given is continuously ebbing away - from maybe an average of three days notice to an average of one days notice to (maybe) an average of half a day's notice. And, to be frank, if Equity had more power in the commercial casting sphere (which they don't unfortunately), I don't doubt they would have deemed such policies basically detrimental to the actor, and have fought against them.
It isn't really a question of preparation time - as the basic requirements of most commercials auditions can, indeed, be got down in about ten minutes - it is more to do with the fact that such short lead times do ensure that actors are at risk of losing job opportunities, alienating their own representatives, jeopardising their 'supporting' jobs by having to leave shifts at extremely short notice and so on. At the end of the day, I hold one of the most flexible jobs it is possible for me to hold (barring literally running my own business affairs), and even I could not make myself available for an audition announced to me the same day if I am already booked to work that day - that it can be assumed anyone can actually do this seems to suggest that the casting directors themselves have bought into the myth of the permanently 'resting' actor, who would appear to have nothing else to do in their life except wait for the next audition to come their way. Still, I play devil's advocate, because I must concede that, when all is said and done, if I am given an audition slot which is all but impossible to cater for so late was notice given, I don't go to it, and I don't lose sleep over it. Particular instances do not negate the fact that the principle in play is extremely questionable, however.
With all this said, and in a sort of (backhanded) defence of CCP in response to Keith's post, there are often breakdowns given on here which demand a very last minute response. In a sense, I feel this is different, because the user is controlling the application process - i.e. if you are available at short notice, can make the audition and see the breakdown at the apposite time, then there is nothing to stop you offering your services for the audition at short notice (and, presumably, being offered a swift reply in return). Often, when a cast member has unexpectedly left a project or a final demand been wangled out of a casting director by an ad exec who has changed their mind about the campaign, a post will be sent here to try and garner applicants quickly and efficiently. I don't imagine you could possibly have managed something like this in the days before the Internet. The issue of short lead time doesn't really become one because the tacit acknowledgment that the actor is available in the first instance goes without saying - if you aren't around you don't apply for it, as simple as that! The issue arises purely when a call to audition is issued at very short notice without giving you enough of a heads up to respond to it.