Wrong. The 2/3 is the total of members in each House not those who are present for a particular vote.
[HOUSE PRACTICE, 108th Congress, 1st Session] [A Guide to the Rules, Precedents and Procedures of the House] [From the U.S. Government Printing Office via GPO Access]
CHAPTER 57 - VETO OF BILLS
Sec. 6 . -- Voting; Disposition of Bill
Under article I, section 7 of the Constitution, a vetoed bill becomes law when it is reconsidered and passed by the requisite two-thirds vote in each House. The two-thirds vote required to pass the bill is two-thirds of the Members voting, a quorum being present, and not two-thirds of the total membership of the House. 4 Hinds Sec. Sec. 3537, 3538; 7 Cannon Sec. 1111. Section 7 further requires that the vote on passage of a bill over the President's veto must be by the yeas and nays. Deschler Ch 24 Sec. 22.10.
The motion to reconsider is not in order on the vote on the question of overriding a veto. 5 Hinds Sec. 5644; 8 Cannon Sec. 2778.
When a vetoed House bill is reconsidered and passed in the House, the House sends the bill and veto message to the Senate and informs that body that it passed by the constitutional two-thirds vote. When the House fails to pass a bill over the President's veto, the bill and veto message are referred to committee, and the Senate is informed of the action of the House. Deschler Ch 24 Sec. 23.
This information can be found on via the House of Representativs at the following link:
http://frwebgate4.access.gpo.gov/cgi-bin/waisgate.cgi?WAISdocID=28098229998+0+0+0&WAISaction=retrieve