Time Expressions Guide

Users rarely speak in ISO 8601. They say "next Tuesday," "end of day," or "sometime this week." Interpreting these expressions correctly requires understanding context and conventions.

Relative Time Expressions

Relative expressions anchor to "now" and shift by some amount. "Tomorrow" means now plus one day, "last week" means the 7-day period ending at the start of this week. The reference point matters — "tomorrow" at 11 PM is very different from "tomorrow" at 8 AM.

Day-relative expressions: "today," "tomorrow," "yesterday" are straightforward but timezone-dependent. "Today" in Tokyo ends before "today" in New York even starts. Always resolve relative day references in the user's timezone.

Week-relative expressions: "this week," "next week," "last week" depend on when the week starts. In the US and most of the Americas, weeks typically start Sunday. In Europe and much of the world, weeks start Monday. ISO 8601 defines Monday as the first day. When interpreting "this week," use the user's locale preference or ask for clarification.

"Next Tuesday" is notoriously ambiguous. If today is Monday, does "next Tuesday" mean tomorrow or eight days from now? Usage varies by region and individual. Some people distinguish "this Tuesday" (the upcoming one) from "next Tuesday" (the one after). When stakes are high, confirm: "You mean Tuesday the 15th?"

Month and year expressions follow similar patterns. "This month" typically means the current calendar month, not "the next 30 days." "Last year" means the previous calendar year. "In two months" is ambiguous — is that 60 days, or two calendar months from the current date?

Fuzzy Time Expressions

Fuzzy times describe approximate ranges rather than precise moments. They require interpretation based on context.

Times of day: "Morning" typically means 6 AM to noon, "afternoon" is noon to 5 or 6 PM, "evening" is 5 PM to 9 PM, "night" is 9 PM onward. But these vary by culture and context — "morning meeting" probably means 9-11 AM, not 6 AM.

"End of day" (EOD) varies dramatically by context. In business settings, EOD often means end of business hours (5 PM or 6 PM local time). In engineering, it might mean midnight. In email, it could mean "before I go to sleep." When a deadline is EOD, clarify the exact time and timezone.

"End of week" (EOW) has the same ambiguity. Does the week end Friday at 5 PM, Friday at midnight, Saturday, or Sunday? Business contexts usually mean Friday end of business. Clarify.

Quarterly references: Q1 is January-March, Q2 is April-June, Q3 is July-September, Q4 is October-December in standard fiscal years. But fiscal years vary — some companies have fiscal years starting in July, April, or October. When someone says "Q3," confirm whether they mean calendar Q3 or their fiscal Q3.

"Soon," "shortly," "in a bit" are context-dependent. A waiter saying "your food will be out shortly" means minutes. A contractor saying "we'll get to that soon" might mean weeks. Don't use these in formal commitments.

Business vs Calendar Time

Business time counts only working hours and days. "Two business days" skips weekends and possibly holidays. "Working hours" typically means 9 AM to 5 PM in the relevant timezone, but varies by industry and company.

Holidays complicate business time. US federal holidays, local holidays, company-specific holidays, and floating holidays (like the day after Thanksgiving) all affect "business days." When calculating business-day deadlines, ask which holiday calendar applies.

24-hour businesses and global teams blur the concept of "business hours." A support team might operate in shifts across timezones, making "business hours" effectively 24/7. Clarify expectations.

Lead times in business contexts often use business days. "3-5 business days for shipping" means weekdays only. But "arrives in 24-48 hours" usually means calendar hours.

Time Ranges and Boundaries

"Last 7 days" can mean different things: the past 168 hours from right now, or the 7 most recent calendar days (including today or not?). When filtering data, be explicit: "from 2024-01-08T00:00:00 through 2024-01-15T23:59:59" or "events in the 7 days prior to today."

Inclusive vs exclusive boundaries matter. "Events from January 1 to January 31" — does that include January 31? Half-open intervals (start inclusive, end exclusive) are a common convention: [Jan 1, Feb 1) clearly includes all of January.

"This week" usually means the current week up to now, not the entire week. Asking "what meetings do I have this week" on Wednesday probably shouldn't include next Friday's meetings. But "schedule something for this week" might include the rest of the week.

Ambiguity Resolution

When time expressions are ambiguous, prefer the interpretation that makes most sense in context. "Can we meet next Friday?" asked on a Thursday probably means tomorrow, not eight days out. "Deadline is end of month" probably means the last business day, not midnight on the 31st.

For high-stakes interpretations (deadlines, appointments, payments), always confirm. Restate the interpreted time: "I've scheduled your meeting for Friday, January 19th at 2 PM Pacific Time. Does that look right?"

When building systems that accept time input, be permissive in what you accept but explicit in what you confirm. Parse "tmrw 3pm," "tomorrow at 15:00," and "Jan 16 3 PM" the same way, but always show the user the interpreted result.

Cultural Considerations

Date formats vary: US uses MM/DD/YYYY, most of the world uses DD/MM/YYYY, and ISO uses YYYY-MM-DD. The string "01/02/2024" is January 2nd in the US but February 1st in Europe. When in doubt, use unambiguous formats: "January 2, 2024" or "2024-01-02."

Week numbering differs. The US rarely uses week numbers; Europe commonly does. ISO week 1 is the week containing the first Thursday of the year.

Working days vary by country. In many Middle Eastern countries, the weekend is Friday-Saturday. In some countries, Saturday is a half-working day. Validate assumptions about "business days" for international contexts.