Evening classes, choir practice and rehearsals all begin whether or not you have arrived, and the journey is usually the part that gets underestimated. This page counts down to 9:40 pm exactly, so the decision about when to leave rests on a number rather than on optimism.
The count makes no sound and asks for no attention while it runs. It is a number, not an alarm, and nothing goes off when it reaches zero. Leaving the page open in a background tab is perfectly fine — it will carry on counting towards 9:40 pm whether or not anyone is watching it.
British speech has a well-worn habit of dropping the middle out of a time: half seven means half an hour after seven, never half an hour before it. Quarter past and quarter to work the same way. Written down, the same moment appears plainly as 9:40 pm, or as 21:40 where no ambiguity is allowed.
Common questions
What is 21:40 in the 12-hour clock?
That is 9:40 pm, or twenty to ten at night if you are saying it aloud. From 13:00 onwards, subtracting twelve gives the pm figure — the same moment written three different ways.
Does the number update by itself?
Yes. It recalculates every second from your device's clock, so there is nothing to refresh or restart. Whatever is on screen is the current gap to the target time, not a figure worked out when the page first loaded.
What happens if 9:40 pm has already gone for today?
The count simply carries on towards the next occurrence, which is tomorrow. That rollover happens on its own — the page does not need reloading and there is nothing to reset by hand.
Which clock does it use?
Your own. It reads the local time and time zone from the device you are looking at, so the figure reflects where you actually are rather than a fixed zone written into the page.