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 5:15 pm precisely, which makes it much easier to judge honestly whether there is enough time left to get there and back.
Coming back to this page in an hour, tomorrow or next month shows exactly the same thing: however long is genuinely left until 5:15 pm 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.
Said out loud, 5:15 pm usually comes out as quarter past five in the evening rather than as a string of digits. Spoken and written time diverge more than people expect, which is worth remembering when somebody tells you a time over the phone and you are trying to match it against something printed.
Common questions
What happens if 5:15 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.
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.
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 5:15 pm, 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.