library(stringr)

txt <- c("SHOW: Game of Thrones 7:00 PM EST", "SHOW: The Outsider 3:00 PM EST", "SHOW: Don't Be a Menace to South Central While Drinking Your Juice In The Hood 10:00 AM EST")
pattern <- "\\bSHOW:\\s+(.*?)\\s+\\d{1,2}:\\d{1,2}\\s+[AP]M\\b"
str_match(txt, pattern)[,2]