Errands at this time of day get squeezed between other things, and the useful question is not what time it is but how much of the middle of the day is genuinely left. This page answers that against 11:59 am exactly, updating on its own for as long as it stays open on the screen.
Because the count reads straight from your device's clock, its accuracy rests on that clock being right, time zone included. Phones and computers normally handle this themselves, so in practice the figure here lines up with whatever time the device is already showing elsewhere on screen.
Writing a time as 11:59 am keeps the am or pm attached, which reads naturally in a sentence but is easy to skim past in a long list of similar entries. Writing it as 11:59 is less conversational and considerably harder to misread, which is why schedules and rotas lean that way.
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 11:59 am 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 11:59 am, set an alarm as well and treat this page as the running total.