Most webcast presentations are scheduled to take half an hour or one hour or multiples of that. If you organize a webcast presentation, think about the timing that it really takes. Always ensure that there is sufficient time planned for the presentation and addressing questions / comments, but also not block too much time.
Your audience will always appreciate when the webcast ends a bit early, like 5 or 10 minutes as it will give them back some time in their day. But, when you end a presentation way too early it will also not look good for you. For example if a webcast presentation is scheduled for 1 hour and it only takes 25 minutes, your audience may start to think that it is bad planning by blocking their calendars for an hour, as they could have prepared / scheduled something else to do in the half an hour that is left over. If the webcast with multiple presentations was scheduled for half a day and it ends 30 minutes early, that may be perfectly acceptable as it should be seen in proportion to the total blocked time for the webcast. So, ensure proper planning and timing of the webcast presentation.