Hi Cerberus,
I decided in advance that I wasn't going to spend too much time on my secondaries, and gave myself a deadline for each one. I tried to get my secondaries in and out in about one to three days, depending on the school. The longest I took was three weeks, and that's mainly b.c I was being lazy since it was the last application and had several essay questions. And I didn't write a story for the essays either. I generally wrote a solid paragraph, which some people may not be comfortable with. If you need to write a monologue to get your point across, then take the time to do that. Otherwise, you communicate what you need to in your AMCAS essay. The secondary essays are put in place to "get to know you better" (i.e. busywork). During interviews, I wasn't asked any questions about what I wrote in my secondaries, only references to my primary essay.
As far as essay construction, I just utilized each school's bulletin, wrote down a few points on why I liked each school, and constructed essays from those notes. The questions are different, but not so different that you can't recycle. I also used some work time (during lunch, down time, or at the end of a long day) to complete the essays as well. I am working, and may not have had as much to do as folks normally do in school, but I also have a relatively easy time with writing.
My advice is not to spend forever and a day on the secondaries. Take Laurie's advice, look up some of the secondary questions, and make a judgement as to whether you'll need a lot of time to do them. Just aim and shoot without hesitating.
Best,
H&T