First, let me qualify this by saying that I am not in any way voicing disapproval or impatience with regards to my own situation; I only stumbled upon this question by musing that my own time in the catechumenate seems like it's going to be fairly short, based on my discussions with my priest. Basically, I'm not complaining at all, and am far too early in the game to even think about doing so. I'm grateful to be where I am!
That said, it seems that there was a break at some point, that a major change occurred in terms of the length of time conversion took. In the bible, and in early anecdotes, there seem to be tons of cases of folks just professing belief in Christ and being on the spot baptized, of whole communities and families converting instantly. There is the story of St. Paul and the Ethiopian...
Then, it seems, from a few patristic sources that I've read, that conversion suddenly became, at times, a multi-year process. Now, it's somewhere in between, 6-12 months, give or take a few months either way, I gather.
Can anyone explain why this changed initially, and why it stands where it does now? Are there modern instances of people, in rare circumstances, being struck with belief and converting on the spot? I don't come from a protestant background, so this is not a familiar scenario to me, but I'm curious nonetheless... I had always had this question while in the RC church, as well, as their catechism process is similar, not in nature, but in length.