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 8:04 pm is that departure, the countdown here gives the exact figure rather than a comfortable guess.
Coming back to this page in an hour, tomorrow or next month shows exactly the same thing: however long is genuinely left until 8:04 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.
Plenty of phones, laptops and dashboards default to a 24-hour display regardless of how people around here actually talk, so 20:04 may well be the figure staring back at you even though 8:04 pm is how the same moment would be said aloud. Neither is more correct than the other.
Common questions
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 8:04 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 8:04 pm, set an alarm as well and treat this page as the running total.