so the posts here make a lot of sense, getting your secondary out after a week of getting them is great. A system that I've been following is this..
If the secondary is easy (ie no essays or 1 essay under 500 characters), send out immediately. This will take you like 1 hr to fill out max, just go to a computer lab and its one less worry on your mind
All other secondaries fall under two categories...
For schools that have rolling admissions, these definitely need to be filled out within a week or two of receiving them. You'll be a lot happier, since you'll interview earlier, get accepted earlier, and then you can save a ton of $$$ by not even attending other interviws if you get into your university of choice
For schools that don't have rolling admissions (which tend to be a lot of the ivy league ones as far as I've noticed), I say take your time filling them out.. there's no real hurry to interview early. Plus, this gives you the added benefit of being able to reuse essays from other secondaries since you're writing these last and you can pick and choose the best ones.
However you decide to do it, just realize that secondaries should not be making you stay up until 3:30 AM writing essays. Take your time, write good stuff, and don't let them stack up on you.
-Cantal