What is on the page, and what is not
If you came here looking for a ticking timer in the header of the registration page, here is the straight answer: a webinar page does not carry one. What it carries instead is the information a guest checks against a diary: the title, the date, the start time with its zone shown as a label beside it, the agenda chapters with their durations, the speaker, the number of places and the form. Those sections decide whether the person signs up; the counting down happens in everything that follows.
A timer, after all, is only ever as convincing as the date underneath it. The reliable version of urgency is exactness: a start time that is real, a stated end, and a page that says plainly whether there are places left. The cap you set is enforced on the page, which shows places remaining and turns to full once your number is reached.