I got a new wire on the bottom today ("Fifteen Twentytwo"?) so that I could get elastics. Good thing I've been reading the Metal Mouth Message Board so much or I would have been quite surprised. I have to wear class II elastics. Changing elastics at least daily, but the assistant said to change them after every meal. The only time I don't have to wear them is when eating or brushing. My ortho didn't say for how long I'll have to wear them, but my next adjustment will be January 11, so that's seven weeks for starters.
There's a picture of the elastics package (The little yellowish round thing being one of the elastics for reference) to the right.