Critics argue about whether or not the play was written specifically for the Twelfth Night. Leslie Hotson argues that Twelfth Night was performed for Queen Elizabeth and her guest, Count Don Virginio Orsino, on January 6, 1601 (Orsino, of course, is Viola's love interest in the play). Some argue that the play was written later, but even those who refute Hotson's argument acknowledge that the world of the play celebrates the spirit of Twelfth Night festivities. Twelfth Night, in Shakespeare’s day, was a holiday celebrated by a festival in which everything was turned upside down. Elizabethan communities often appointed young boys as "Lords of Misrule"; it was a chance to play king for a day - much like the upside-down, chaotic world of Illyria. This rebellious spirit is reflected in figures like Sir Toby Belch and Sir Andrew Aguecheek, alongside Feste's singing and comedy.
Some theorize that the second part of the title was an afterthought: when someone asked the playwright "the name of the play, Shakespeare replied, "Urm, Twelfth Night, or what you will" (as in, "I don't know – whatever"). The second title seems to invite the audience to make "what [we] will" of the play – what it means, and why it matters (if it matters at all) - it is entirely subjective.
Some directors of the play have taken the title literally, paying close attention to the Elizabethan rituals related to Twelfth Night; others have disregarded it entirely, and set the play in the sunny Mediterranean, where the historical "Illyria" is located or, as we have done, in 1920s England.