Sometimes in the flurry to plan an event, such as a web conference, many details are left unattended. This can happen to any organization, whether it is their very first web conference or they hold such an event every week.
Take some time to think about all that is involved, make lists, and divide up tasks. Do what you have to so that you can be assured that things will run smoothly.
You have no control over attendees' schedules, but you can make sure that the timing is coordinated. If you have participants in different parts of the U.S. or different parts of the world, you need to be certain that everything is set for the right people at the right time.
It is quite possible to get into a tizzy about speakers, technology, topics and other matters, forgetting that time is of the essence.
Also, be certain to inform participants not only of the time, but also of the duration of the web conference. It is so easy to concentrate on getting the start time correct, that you omit to advise people of how long they are expected to attend. You want key people to be able to take part in the entire web conference, so give them advance notice to clear time on their schedules.