Counters and branches that close in the late afternoon give no leeway at all, and arriving two minutes late means coming back tomorrow. This page counts down to 3:15 pm precisely, which makes it much easier to judge honestly whether there is enough time left to get there and back.
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 3:15 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 3:15 pm, or as 15:15 where no ambiguity is allowed.
Common questions
Is it affected by the clocks changing?
Only in the sense that your device is. When the change between GMT and BST happens at the end of March and October, the device adjusts and the countdown follows it without anything to do here.
What is 15:15 in the 12-hour clock?
That is 3:15 pm, or quarter past three in the afternoon 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 3:15 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.