Day 7, or as soon as your starter is established
At this point the starter should be active, with bubbles breaking on the surface. Touch it, and you will find that gluten has developed; it should beel somewhat elastic. It is ready to be used, or placed on one of the two maintenance schedules that follow.
My favorite cookbook of all time--The King Arthur Flour Baker's Companion--and Gushy, my favorite (and only) starter of all time did not let me down. Together, they yielded an airy, complex, flavorful, crusty sourdough that was unlike any bread I've ever baked (and I've baked a lot of bread)! Gushy is still happily bubbling away, and I look forward to adding him to whole wheat bread, waffles, and many more future delicacies.