GlobeTime / Learn & practise
Time Challenge
Set the clock, cross time zones and solve five time missions. Explore at your own pace and understand each result.
Choose your session
The same five questions to share
Everyone opening the same dated link gets the same questions, in any language. No leaderboard or account.
A fresh set whenever you want
Choose a route with varied situations and balanced answer cards. Set the clock yourself or use the alternatives.
Answers stay in this open page only. Refreshing, changing language or ending the session resets them. Nothing is saved automatically.
Understand time formats and clock calculations
Use this activity to check AM/PM conversions, practise reading 24-hour schedules and work out start or finish times. Every answer includes its reasoning; there is no timer or speed bonus.
How to play the time missions
Complete five missions by setting an interactive clock. Select hours or minutes and tap a dial number, use precise adjustment buttons, or type a 24-hour time. Choose AM/PM and check the date before confirming. The clock reveals the correct result and a worked explanation after each attempt. Four answer cards remain available as an alternative. Foundations practice uses quarter-hour starting times; Explorer adds arbitrary minutes in clock calculations and a time-zone mission across a seasonal clock change. Daily links retain their original questions and alternatives. No account, countdown or penalty for taking your time.
Example: a finish time after midnight
Start at 22:50 and add 1 h 25 min. Adding minutes gives 23:75, which becomes 24:15 after carrying 60 minutes into an hour. The result is 00:15 the next day. Giving only 00:15 would omit part of the answer.
What these exercises calculate
The formats/calculations module uses civil clock calculations: an exercise day contains 24 hours and does not model daylight saving changes. For a real trip or meeting, use the time zone converter with the actual date. Formats use 00:00–23:59; 24:00 is not an answer option.
Daily sets use a visible UTC date from the device clock and a versioned generator. A dated link keeps the same questions across languages, even if you open it later. Free practice creates another set. Reloading or changing language starts a new session.
How city situations work
Practise a call from Tokyo to Los Angeles, a London–Kolkata conversion, Paris–New York in March and a 90-minute event across a New York clock change. Read the reference date before answering: the destination may be on a different day. The March example uses the rules of its specific year; countries do not always change their clocks together.
City situations convert an explicit UTC instant using the bundled IANA database. Event durations are added in UTC before conversion, so a skipped or repeated local hour does not change the elapsed duration. Dates are written with a month name; UTC offsets distinguish repeated hours. Hints are optional and there is no time limit.
City links use v2 and identify their IANA version. If that version is no longer available, the link is rejected rather than silently changing its answers. Use the current challenge to start again. The original format/calculation links remain v1. · IANA 2026f