Found the following on line
Watchtower article on joining Disapproved Organizations
A person might renounce his place in the Christian congregation by his actions, such as becoming part of an organization whose objective is contrary to the Bible, and hence is under judgment by Jehovah God. (Compare Revelation 19:17-21; Isaiah 2:4) So if one who was a Christian chose to join those who are disapproved of God, it would be fitting for the congregation to acknowledge by a brief announcement that he had disassociated himself and is no longer one of Jehovah's witness - The Watchtower, September 15, 1981 page 23.
Here is a quote from “Prayer and Mediation At The United Nations” (The Watchtower 1 st June 1991 describes this a an excerpt from a recent book by Robert Muller).
"Prayer, meditation and spirituality at the UN are fascinating subjects. All major world religions are accredited to the United Nations as non-governmental organizations. For example, no less than twenty-four Catholic organizations are represented at the UN. Several of the world's religious leaders have visited the international organization. Most memorable were the visits of His Holiness Pope Paul VI during the General Assembly in 1965 and of Pope John Paul II in 1979. Many religions have special invocations, prayers, hymns and services for the United Nations. The most important examples are those of the Catholic, the Unitarian-Universalist, the Baptist and the Bahai faiths. It is a common practice of the Unitarian-Universalists to display the United Nations flag in their houses of worship. So does the Holy Family Church, the parish church of the UN, with its international reliquary and its many religious services and activities catering to world peace and to the international community.”
The whole of the above less the underlining was quoted in the Watchtower Magazine of 1 st June 1991 on Page 17. But the underlined part of course is the crucial quote. It defines precisely what it means for a harlot church to ride the beast. Very simply you saddle up by becoming an associated NGO. There is no other mechanism for a religious organization to join the UN in order to ride the beast.
So the Watchtower saddled up on January 28 th 1992 and dismounted on October 9 th 2001.