Thats a tough question because on one hand, you want to give the letter writer adequate time for writing a good letter, on the other hand, schools sometimes have specific questions the writer must answer, and they don't accept any substitutions. Michigan St., Ohio, LECOM (I think) had specific questions the writer had to answer. CCOM, AZCOM, Western U.,NYCOM, and PCOM were schools I applied to that just had a straightforward letter requirement with no goofy questions that make it tough on the letter writer. Michigan state was damn specific with its questions. ALso, make sure you have two science faculty, this includes physics, bio, chem, biochem, anatomy, physiology, etc. They are very specific with this, they don't accept calculus or math profs, so plan for this.
