"Then be not coy, but use your time, / And while ye may, go marry;"
--Robert Herrick, "To the Virgins, to Make Much of Time"
When I first began teaching, I tried desperately to stay 2 weeks ahead of my classes. But no matter how I hard I worked to keep my planning and heading on that time curb, it never happened. I always found myself scrambling to get lectures and class activities together the day of or (even worse) while in class.
Now that I have a better sense of a semester's rhthym, I am much better prepared. But I'm still not quite 2 weeks ahead. Sometimes, it's a week; sometimes, it's a few hours. But that's okay. In fact, I think it's best. Two weeks ahead may be too much. If my preparation is too far removed from the day it is intended for, the timing of my ideas can ebb. My intimacy with a text--even one I've taught many times--isn't as personal as I'd like, which effects the syncronicity of my performance.
The energy, even urgency, created by the close proximity of class preparation and in-class appearance may help bring forth a sense of immediacy, an immediacy perhaps lost when the lecture's been prepared weeks ahead of schedule.