Question: When did the man dubbed  "the most influential private citizen in the America of his day" hire Elmo Roper?

Context articles: Committee of 100 on the Federal City
Elmo Roper
Private rights
Henry Luce
Hannah Carter Japanese Garden
Roper Center for Public Opinion Research
Centro Universitario Anglo Mexicano
Citizen suit
Glik v. Cunniffe
Long Pond (Lakeville, Massachusetts)

The Committee of 100 on the Federal City, locally referred to as the Committee of 100, is a private, nonprofit membership organization which promotes responsible land use and planning in Washington, D.C., and advocates adherence to the L'Enfant Plan and McMillan Plan as a guide to city growth.
 It is one of the most influential private land use planning bodies in Washington, D.C.
Elmo Burns Roper, Jr. (July 31, 1900 in Hebron, Nebraska – April 30, 1971 in Redding, Connecticut) was a pollster known for his pioneering work in market research and opinion polling.
 In 1933, he cofounded Cherington, Wood, and Roper, a marketing research firm.
 When that partnership fell apart, he founded his own research company, Elmo Roper, Inc.
 He was hired by Henry Luce in 1935 to run surveys for "Fortune", continuing these surveys for 15 years.
 His prediction of Franklin Delano Roosevelt's electoral victory over Alf Landon in 1936 was correct to within 0.9%; his 1940 prediction of Roosevelt's victory was correct to within 0.5%, further solidifying the reputation of Roper's techniques.
 In 1940, Roosevelt hired Roper to assess public opinion of Lend-Lease prior to its implementation.
 In 1942 he was hired by William Joseph Donovan to be the deputy director of the Office of Strategic Services; Roper subsequently worked with the Office of War Information.
 After leaving the OWI he founded the Roper Center for Public Opinion Research at the University of Connecticut in 1947.
In the United States, a private right is one that a private citizen can vindicate in court.
 Compare public rights.
 There must be a private right for a citizen to have a claim.
 To have a private right of action, a citizen must be able to show that He/she has "sustained or is immediately in danger of sustaining some direct injury" and not that He/she "suffers in some indefinite way in common with people generally."
 Frothingham v. Mellon, 262 U.S. 447, 488 (1923).
 a distinction between criminal rights and "private rights," arguing that restrictions against ex post facto laws were not designed to protect citizens' contract rights.
Henry Robinson Luce (April 3, 1898 – February 28, 1967) was an American magazine magnate who was called "the most influential private citizen in the America of his day".
 He launched and closely supervised a stable of magazines that transformed journalism and the reading habits of upscale Americans.
 "Time" summarized and interpreted the week's news; "Life" was a picture magazine of politics, culture, and society that dominated American visual perceptions in the era before television; "Fortune" explored in depth the economy and the world business; and "Sports Illustrated" explored the motivations and strategies of sports teams and key players.
 Counting his radio projects and newsreels, Luce created the first multimedia corporation.
 He envisaged that the United States would achieve world hegemony, and, in 1941, he declared the 20th century would be the "American Century".
The Hannah Carter Japanese Garden is a private Japanese garden located in Bel Air, Los Angeles, California.
 Known as Shikyo-en when completed in 1961, it emphasizes water, stones, and evergreen plants.
 The naturalistic hillside site features streams, a waterfall, a tea house, and blooming magnolia and camellia trees.
 According to the Los Angeles Conservancy, the garden is among the largest and most significant private residential Japanese-style gardens built in the United States in the immediate Post-World War II period.
 The garden was donated to the University of California, Los Angeles in 1965 and open to the public until 2011.
 Following a legal dispute with Hannah Carter's children, it was sold to a private citizen in 2016.
The Roper Center for Public Opinion Research at Cornell University is one of the world’s leading archives of social science data, specializing in data from public opinion surveys.
 The Center’s mission is to collect, preserve, and disseminate public opinion data; to serve as a resource to help improve the practice of survey research; and to broaden the understanding of public opinion through the use of survey data in the United States and abroad.
 Founded in 1947 by Elmo Roper, the Roper Center holds data ranging from the 1930s, when survey research was in its infancy, to the present.
 Its collection now includes over 22,000 datasets and adds hundreds more each year.
 In total, the archive contains responses from millions of individuals on a vast range of topics.
Centro Universitario Anglo Mexicano (Anglo Mexican University Centre) is one of Mexico's top leading private co-ed high school and junior high school founded in 1974, that operates in Mexico City, Federal District, Cuernavaca, Morelos, Cancún, Quintana Roo and Mérida, Yucatán having earned a reputation of high academic standards with an emphasis in project research, and a strong athletic program, which has allowed them to have preferential access to the most influential private universities in Mexico.
In the United States, a citizen suit is a lawsuit by a private citizen to enforce a statute.
 Citizen suits are particularly common in the field of environmental law.
Glik v. Cunniffe, 655 F.3d 78 (1st Cir.
 2011) is a case in which the United States Court of Appeals for the First Circuit held that a private citizen has the right to record video and audio of public officials in a public place, and that the arrest of the citizen for a wiretapping violation violated his First and Fourth Amendment rights.
 The case arose when Simon Glik, a private citizen, filmed Boston, Massachusetts, police officers making an arrest in a public park.
 When the officers observed that Glik was recording the arrest, they arrested him and he was subsequently charged with wiretapping, disturbing the peace, and aiding in the escape of a prisoner.
 Glik then sued the City of Boston and the arresting officers, claiming that they violated his constitutional rights.
Long Pond is a lake within the towns of Lakeville and Freetown, in southeastern Massachusetts.
 It shares its waters with Assawompset Pond.
 These lakes provide a source of drinking water to the city of New Bedford, the largest city in southeastern Massachusetts.
 Long Pond is roughly one mile wide by four miles long, and contains three islands within its boundaries.
 In 1894 Assawompset Pond was dammed, increasing the water depth of Long Pond (which is connected by a small river) by about five feet.
 This created Nelson Island and caused Sunken Island to disappear due to erosion.
 All that remains of Sunken Island are the rocks in a shallow area just to the northwest of Lewis Island.
 Lewis Island is the largest of the three remaining islands today, containing sixteen privately owned cottages, while the second largest island, Nelson Island, was purchased in 2005 and now is a year-round private residence.
 The smallest island, Goat Island, was recently purchased from the Boy Scouts by a private citizen.
 Along the perimeter of the lake are many homes and private access points to the waterfront.
 Long Pond is well known for fishing and boating.