My turn around time for each secondary was no more than one week. I would have up to 12 schools lined up on my shelf and in an almost chronological order of when they arrived. (I applied to 34 schools and only returned about 25 secondaries). They began to arrive about one month after my AMCAS went in and they came pretty consistantly every day to every 3rd day for about 2 months. I was going nuts try to juggle the checks, the letters of recs, the writing of the essays and the typing of the secondaries. Many secondaries require you to relist (ie. type onto the original form application) your premed courses including English and Calculus/Math, plus their grades. It can be time consuming to type up all that information for all those secondaries.
Those schools who only want a check (like Boston Univ), will get a turn around time of "same" day and I USPS Priority mail with confirmation of delivery of everything ($3.55, 2-3 days to arrive).
Even though you have to type your personal information onto the original form of the secondary (name, birth place, premed courses etc)...I rarely typed the essays on the secondary. I became very creative with the fonts (usually a 10 font, but I went as small as an 8 font for some schools because their application had limited space) and printer options on my computer and finally, I would have a copy of my printed essay on paper. I would then take that copy and xerox it onto the original secondary application so that it looks neat. Sure, I killed a million trees in the process, but I always recycle my paper products anyways.
Some schools have the one question secondary...please share something about yourself that you think that admissions committee would like to know...or something along those lines. I tended to write a one page essay (font 10, single spaced) that's pretty generic and recycle the same essay for most of the schools with this question.
Then there are schools with specific questions...Rush comes to mind. I must have spent about 10 hours writing the Rush application. One cool thing about secondaries is that it really makes you reflective and even proud of how far you've come when you critically evaluate yourself for those essay questions....what are some things you did for your community? What are some problems you've encountered in school, academic and personal..how did you deal with those problems....what are your strengths and weaknesses? (Old trick known by all....your weakness is really a hidden strength...."I tend to concentrate too hard on one job at hand, which is good when I need to get the job done, I can be sure that I can accomplish that, but it is a disadvantage when I need to perform several tasks, which is why I have learned to budget my time and energy...." See how that weakness became two strengths?).
Oh yeah, have your friend get a camera and take about 15 pictures of your smiling face and then get double exposures of them at the photomat. Then cut each out to passport size. You'll need about 1-2 pics for most secondaries. Real passport photos are ridiculously expensive (like $25-$50 for a set). My way will cost you about $10 for 30+ pictures.
I'm sure you're already planning to do this, but photocopy all your secondaries and keep a copy for yourself.