For example, for Delaware corporations, Section 231(c) of the DGCL provides: "The date and time of the opening and the closing of the polls for each matter upon which the stockholders will vote at a meeting shall be announced at the meeting. No ballot, proxies or votes, nor any revocations thereof or changes thereto, shall be accepted by the inspectors after the closing of the polls unless the Court of Chancery upon application by a stockholder shall determine otherwise."
Although it seems relatively clear, this rule is subject to different interpretations. One interpretation is that this rule requires an announcement at the time the polls are open, that the polls are open, and an announcement at the time the polls are closed, that the polls are closed. Another interpretation, and which in my view is better, is that the chairperson should announce at some point before the polls actually open and before they actually close, that the polls will be opening and closing. The purpose being is to give those in attendance fair notice that if they want to vote, they need to do so, and to avoid any potential claim that their right to vote was unfairly denied. You might even consider adding a statement before the polls close along the following lines: "The polls will be closing shortly. Please raise your hand if you wish to vote and have not had a chance to do so. [Pause to see if any hands are raised.] Not seeing any hands raised, and seeing that all stockholders who wish to vote have had a chance to do so, it is now 10am on May 2, 2013 and I declare the polls to be officially closed."
Believe it or not, lawsuits have been filed regarding the opening and closing of polls, and last year I worked with a company seeking to exclude a stockholder proposal from the company's proxy statement regarding the opening and closing of polls, which proposal was submitted because the stockholder claimed its right to vote was unfairly denied due to annual meeting procedures.