How a time link works
The link names a wall-clock time in a place, as you would say it: 15:00 in London on Friday 16 October. When someone opens it, Hourora works out that instant from the official time-zone rules (IANA tzdata) and shows it on their own clock, with a live countdown.
Because the rules include daylight saving time, the link stays right even when a clock change falls between today and the date you chose, in either place.