One timeline.
No hidden assumptions.

One absolute moment, several local clocks

The date and time controls always use UTC. We combine them into one UTC instant, then convert that same instant to each selected IANA time zone. Your computer's local time zone does not change the meaning of these inputs.

A named zone such as America/New_York describes a set of time rules. A UTC offset describes the difference from UTC at a particular instant. The offset can change with daylight saving or a change in local rules, so the planner shows the local date, time and offset together.

Why we ask for UTC

At a seasonal clock change, some local wall-clock times are skipped and others occur twice. A UTC input gives the first version of this tool an unambiguous reference. We do not interpret typed local dates in a base city or guess which occurrence of a repeated hour you intended.

If you are starting with a local appointment, first obtain its exact UTC time or an invitation containing an explicit offset. Do not assume a remembered city-to-city difference applies on the selected date.

The grid is one UTC day

The 48 columns represent 00:00, 00:30, and every half hour through 23:30 on the chosen UTC date. A column is the same instant across all locations. It is not a view of the same local calendar day in every city: one row can begin on the previous date or end on the next.

Each row shows the local clock hour at hourly marks. Hover or focus a grid button to read its full accessible label, including local date, time and UTC offset. Select a column to update the local clock cards and meeting plan. The selected border represents the half-hour block containing your chosen time; the cards retain its exact minute.

Work windows are daily, local and end-exclusive

Each location has its own start and end in local wall-clock time. The start is included; the end is excluded. A 09:00–17:00 window includes 09:00 and 16:59, while a meeting starting at 17:00 is outside it.

Windows repeat every day. We do not infer weekdays, public holidays, leave, breaks or personal commitments. A green cell indicates that the start of that cell is inside the work window. It does not confirm availability for an entire meeting.

Suggested meetings check the full duration

Candidate starts are spaced 30 minutes apart within the chosen UTC day. For every candidate we check each occupied minute of the selected duration against every local work window, using that minute's correct zone offset. The meeting end is exclusive, so a 60-minute meeting may finish exactly at the work window's end.

A candidate may continue beyond UTC midnight if every participant's daily window allows it. The starting instant belongs to the displayed UTC date; the meeting plan states the start and duration. Candidate starts are suggestions, not an exhaustive search of every possible minute. A 09:15 start can still be inspected with the UTC time input.

Time zone data and verification

Conversion uses Luxon with your browser's native Intl time zone support. The IANA Time Zone Database is the reference system for the named zones. Browser and operating-system data can lag behind changes in government rules; keep them updated and recheck future meetings near the date.

The automated domain tests cover US/UK seasonal change differences, skipped and repeated hours, fractional UTC offsets, date boundaries, cross-midnight windows, complete meeting durations and invalid input. The project README records how to run them. Browser interactions and printed output should also be checked before deployment.

Your next step

Use the grid to make a clear proposal, then confirm it with participants and send an invitation through your normal calendar. We do not connect to calendars, reserve a room, notify participants or verify an attendee's availability.