The webinar will not be live for the audience until your presenter clicks on the "Start presenting" button in the presenter screen.
While presenters may occasionally start a few minutes late, keep in mind that the countdown for the remaining duration of the event begins at the scheduled start time. This means you have less time to present if you begin later than scheduled.
Please note: every webinar has an additional 4 minute over-run period which extends beyond your scheduled duration.
i.e a 60 minute webinar can run to a maximum of 64 minutes, including the over-run period.