This is not an official timeline.  I only matched it up based on dates gathered playing the game.

This timeline contains spoilers

According to the Japanese main site, Iris is 30.  Her story in the game puts her age at 28.  For this timeline I went with 28.

There's also a lot missing, but the game isn't always good about giving specific dates

 
1933 Robert Evans inherits Gallery May from his grandfather at the age of 23.
1959 Hotel Dusk is built and opened.  Helen is reunited with her son, Allen, when she is hired to perform at the opening
1960 A plan crash in Las Vegas kills Mrs. Dunning, Mary Evans, and Iris and Grace's mother.  Dunning and Evans are reunited after having split up after college.  They develop a plan to sell Dunning's art
1963 Robert Evans writes a book about the life of the fictional painter, Osterzone.  His and Dunning's success gets them noticed by crime syndicate Nile
1966 Iris runs away from her adoptive parents.
1969 The "Seven Stars" bar is opened to celebrate the hotel's 10 year anniversary.

Helen again meets Allen at Hotel Dusk, before it is closed

Jenny Smith is kidnapped by Nile to blackmail Dunning into painting more.  Evan's daughter Mila falls into a coma

Summer steals Allen's manuscript, "The Secret Word" and has it published under his name
1971 Iris gets a job at a diner in Santa Monica, and is briefly reunited with her sister Grace.  Grace was engaged to Kevin at the time.
1972 Gallery May in Santa Monica is closed.   Evans sends Dunning a letter telling him to be patient, but then disappears
1973 Grace finds work at an art museum.
1974 Dunning reopens Hotel Dusk and combats rumors about it by spreading stories about room 215 granting wishes
1976 Bradley goes undercover within Nile, and though he discovers the truth about Osterzone, Evans, and Dunning, he's found out and his sister Mila is taken hostage.  Nile blackmails him into betraying the cops and killing one of their own, Danny.

Kyle, thinking that Bradley betrayed the force to work for Nile, shoots him on the docks.  Bradley disappears

Louis DeNono skips town after witnessing Danny's murder
1977 Kevin Woodward loses a big malpractice case.  Him and his wife start having problems
1979 (June) Bradley kills Evans, then visits Dunning at Hotel Dusk on June 30th.

Grace sends a cassette tape incriminating Dunning and Evans in the Osterzone scandal to her sister, Iris.  She then leaves her husband and daughter, vanishing.
1979 (December) Hotel Dusk: Room 215 takes place