On 25 October 2017, user Tenlade#9234 pointed out in the Doki Doki Fan Club Discord Server that the background of Sayori's room had a higher resolution version on background artist Velinquent's Pixiv account. The calendar very clearly reads "Calendar 2017" in English, which has some interesting implications.
First day of the week
The first day of the week varies around the world. In most countries, Monday is the first day of the week. In the Middle East (using the Islamic calendar), the first day of the week is commonly Saturday. In the United States, Canada, most of Latin America, India, Japan, Taiwan, Hong Kong, Macau, Israel, and South Africa, the first day of the week is Sunday.
As Doki Doki Literature Club! takes place in a faux-Japan and was made in the United States, I had previously assumed that the first day of the week would be Sunday.
However, Discord user Schiller#6842 matched the calendar in the image more accurately to one which begins with Monday. This is likely due to the fact that the artist who drew the backgrounds Velinquent is from Ukraine, a country wherein Monday is the first day of the week.
The calendar displays all twelve months in a 3x4 grid, and the headings for each month can barely be inferred through the small, pixelated text on the image. Each month is displayed in a 8x7 grid. The extra row can be explained by the presence of "Mo Tu We Th Fr Sa Su" on many calendars and the extra column is to mark the week number. These are the 14 red markings present on the calendar:
- Circle, circling the "Monday" cell on the January grid.
- Circle, Wednesday, 4 January 2017. Near the beginning of the final trimester of the Japanese school year.
- Circle, Friday, 27 January 2017 or Saturday, 28 January 2017
- Circle, Saturday 25 March 2017. Near the end of the final trimester of the Japanese school year.
- Circle, target unclear. Either circling the "Wednesday" cell on the August grid, or circling Wednesday, 2 August 2017.
- November is scribbled over.
- Sunday, 1 January 2017 is red.
- Monday, 16 January 2017 is red.
- Friday, 20 February 2017 is red.
- Monday, 29 May 2017 is red.
- Monday, 4 September 2017 is red.
- Monday, 9 October 2017 is red.
- Thursday, 23 November 2017 is red.
- Monday, 25 December 2017 is red.
Additionally, the bottom right corner of the calendar is torn out, ripping through an extra section at the bottom with an unknown purpose. Perhaps it's a space meant for detailing extraneous holidays or events or something.
The specific dates on which the game takes place are unclear, but there are a few indicators to go off. Firstly is the idea of the cultural festival, a staple of Japanese schools. They often show off the work of the students of the school, sometimes including that of the school's clubs. The festival often takes place around 3 November, a national holiday called Culture Day. However - unlike the festival in DDLC, cultural festivals generally take place on Saturday, Sunday, or both.
The timeline of the game begins on a Wednesday and ends on the following Monday. Fitting this timeframe closest to Culture Day in 2017 yields the date of Wednesday, 1 November 2017 to Monday, 6 November 2017. A wrinkle in this placement, however, is the obvious lack of any holiday on the Friday in-game (or even a holiday mentioned at all in the game, for that matter). This is made more confusing by the faux-Japan which the game is set in, making it unclear if the school system works by USA timeframes or Japanese ones.
Monika's Twitter account has made some tweets of note that could be useful.
- Tuesday, 14 February 2017: "today's my favorite day!!!!! ❤️❤️❤️❤️❤️"
- Wednesday, 22 February 2017: "i'm bored..."
- Sunday, 19 March 2017: "it's so sad when you have friends who you can tell really want to share their emotions but they don't know how..."
- Wednesday, 10 May 2017: "If I can't hear the sound of your heartbeat / What do you call love in your reality?"
- Friday, 19 May 2017: "i heard that some people have been talking about the literature club!!! maybe we'll be getting new members soon? o(>ω<)o"
- Monday, 26 June 2017: "reducing meat consumption is an easy way to help save the world!"
- Saturday, 9 July 2017: "i don't have a scary-looking face, do i...? i wish i could figure out how to be more approachable"
- Sunday, 15 July 2017: "umm, what does it mean for someone to be "in beta"? i keep hearing that???"
I'm reluctant to make any conclusions from these dates.