The last train back is the one time in an evening that genuinely will not wait, and working backwards from it is how people end up leaving earlier than they meant to. If 6:09 pm is that departure, the countdown here gives the exact figure rather than a comfortable guess.
When the clock reaches 6:09 pm, the count does not sit at zero. It rolls straight over and begins again towards the same time tomorrow, on its own, without a refresh or a reset. That makes this a page worth keeping in a bookmarks bar rather than one you look at once and forget.
Between the last Sunday in March and the last Sunday in October the country runs on BST rather than GMT, which is why timetables and confirmations sometimes carry the label as well as the number. This page counts down to 6:09 pm using whatever your device is currently set to, so the switch is handled for you.
Common questions
What is 18:09 in the 12-hour clock?
That is 6:09 pm, or nine minutes past six in the evening 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 6:09 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.