Question: What year did a barbershop quartet begin performing in a theme park that opened on July 17, 1955?

Context articles: Max Q (quartet)
Realtime (quartet)
OC Times
Mid-Atlantic District (BHS)
Disneyland
The Dapper Dans
Bluegrass Student Union
Ringmasters (barbershop quartet)
Four Hearsemen
Vocal Spectrum

Max Q is the barbershop quartet that won the gold medal Barbershop Harmony Society International Barbershop Quartet Contest at Denver's Pepsi Center July 7, 2007.
Realtime is a barbershop quartet that won the Barbershop Harmony Society's International Quartet Championship in 2005.
 They finished seventh-place the previous year (the first ever top-ten finish for a western-Canadian quartet).
 Lead singer John Newell is the first Australian-born international champion.
 Baritone Mark Metzger and bass Tom Metzger are the first champions who are both Canadian-born and Canadian citizens.
 Tenor Tim Broersma is from Lynden, Washington.
 In 2008, Doug Broersma became the lead singer when Newell retired for family reasons.
 The quartet was succeeded by Via Voice when Tim Broersma retired in 2011, also for family reasons.
OC Times is a male barbershop quartet affiliated with the Barbershop Harmony Society.
 They earned second place silver medals at the International Barbershop Quartet Contest at Denver's Pepsi Center on July 7, 2007, and won the International Quartet Championship on July 5, 2008 in Nashville, Tennessee.
 The quartet combines traditional barbershop harmonies with contemporary music styles.
 The music of OC Times is inspired by artists like Michael Buble, Sinatra, and Elvis.
The Mid-Atlantic District is one of 17 districts of the Barbershop Harmony Society (formerly known as SPEBSQSA or the Society for the Preservation and Encouragement of Barbershop Quartet Singing in America).
 The district, with three regional divisions, has approximately 90 chapters in the following states: VA, MD, PA, NJ, DE, DC, WV, NY.
Disneyland Park, originally Disneyland, is the first of two theme parks built at the Disneyland Resort in Anaheim, California, opened on July 17, 1955.
 It is the only theme park designed and built under the direct supervision of Walt Disney.
 It was originally the only attraction on the property; its official name was changed to Disneyland Park to distinguish it from the expanding complex in the 1990s.
The Dapper Dans are a barbershop quartet that performs at Disneyland in Anaheim, California (since 1959), at the Magic Kingdom at the Walt Disney World Resort (since 1971), and at Hong Kong Disneyland in Lantau Island, Hong Kong (from 2005 to 2008).
 A quartet (from the UK) also performed at Disneyland Paris from the opening in 1992 until 1995 and were known as the Mainstreet Quartet.
Bluegrass Student Union is the Louisville, Kentucky barbershop quartet who won the 1978 SPEBSQSA International competition.
 They distinguished themselves by performing at a high level of proficiency on stage and in the recording studio throughout their 33-year career, by becoming the second youngest quartet to win the SPEBSQSA championship, and by continually improving their art, even after winning their gold medals.
 They credit much of their success to their coaches, Mary Jo Hatton Thompson, Don Clause, Ron Riegler, Gene Stickler and Ed Weber, to their chorus Director, Jim Miller, and to their long-time arrangers, Ed Waesche and Walter Latzko.
Ringmasters is a Swedish barbershop quartet affiliated with the Society of Nordic Barbershop Singers (SNOBS).
 The quartet received first place gold medals at the Nordic Barbershop Quartet Contest in Stockholm (April 2008), and won the Barbershop Harmony Society International Collegiate Championship in July 2008 in Nashville, Tennessee.
 On July 8, 2012 at the Society's International Convention in Portland, Oregon, they became the first quartet from outside North America to win the prestigious gold medal as International Quartet Champions.
 The quartet sings non-traditional barbershop harmonies with a contemporary touch.
The Four Hearsemen is a Barbershop quartet that won the 1955 SPEBSQSA international competition.
 The Four Hearsemen, a champion Barbershop Quartet, were from Amarillo, Texas.
 The members were: Wendell Heiny, Deane Watson, Dwight Elliott, and Dick Gifford.
Vocal Spectrum is a barbershop quartet from St. Charles, Missouri.
 In 2004, Vocal Spectrum won the Barbershop Harmony Society's International Collegiate Quartet Contest, and on July 8, 2006, they became International Champions, winning the society's International Quartet Contest.
 A distinctive factor of the quartet is tenor Tim Waurick's ability to sustain notes for upwards of 30 seconds, and the tenor's and lead's incredibly high note range, featured in many of the group's recordings and live shows.