Early flights come with a chain of times attached — the cab, the bag drop, the gate — and every one of them sits well before the first trains run. If 12:10 am is the moment the front door has to close, this page counts down to it precisely, so nobody has to keep working it out in a dark hallway.
Coming back to this page in an hour, tomorrow or next month shows exactly the same thing: however long is genuinely left until 12:10 am next comes round. There is no session to lose and nothing to configure again, because the number is worked out fresh each time from the clock on your device.
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 12:10 am using whatever your device is currently set to, so the switch is handled for you.
Common questions
Will this alert me when the time arrives?
No. It is a live number rather than an alarm — nothing rings, buzzes or notifies you at zero. If you need to be interrupted at 12:10 am, set an alarm as well and treat this page as the running total.
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 00:10 in the 12-hour clock?
That is 12:10 am, or ten past twelve 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.