The join button appears 5 minutes before the scheduled start time. At the scheduled start time, the label changes to inform you that the meeting is starting now. When someone else joins the meeting, the countdown appears on the button and you can see how many people have already joined.
The join button appears before the scheduled start time only if you're using the Cisco Webex Hybrid Calendar Service and Microsoft Exchange, Microsoft Office 365, or G Suite for Google Calendar.
The join button doesn't appear before the start time for meetings associated with spaces of more than 200 people.
If you're joining a Webex and TelePresence meeting (CMR Hybrid meeting) or a Webex event, Webex training session, or Webex support session, when you click on the join button the Webex Meetings app opens.
Go to Spaces and click the green button beside the space or meeting name.
Select Device Options and then choose one of the following:
If you selected My Computer, click to choose the audio and video options you want to use:
Click Join Meeting.