I trade both the close and the open when it suits.
Trading the close means placing your order after 4.00pm as sydney suggests but the window of opportunity is almost 10 minutes with my common garden variety Etrade interface. The close comes at 4.10pm although it seems to vary a bit. Most of the order volume will be placed (or pulled) very close to the close so the price isn't as predictable as one might wish.
LYC Price at posting:
16.5¢ Sentiment: Buy Disclosure: Held
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(20min delay)