A lot of planned webcast presentations tend to be scheduled to start at the top of the hour, for example 09:00 AM , 11:00 AM or 16:00 PM. This leaves many people with having back-to-back calls, webcasts, etc. When organizing a webcast you should consider if it is really needed to get it started at the top of the hour.
Consider for the planning of a webcast presentation if you need it to start at the top of the hour. Would sending and invite for the webcast that blocks time starting at 10:15 AM or 14:10 PM also be an option. This may leave your audience with some time before the start of your webcast to get organized / have a break as many other planned meetings will start and stop at the top of the hour.