Google Calendar’s default meeting length time is set to 6o minutes but if you believe short meetings are more efficient you want to change the default meeting time to 30 minutes then you can do using the Calendar Settings.
Click the options menu and select Calendar Settings from the displayed list. In the Calendar Settings page navigate to Default meeting length section under General tab.
Using the time drop down you can set the default meeting to 30 minutes. Google Calendar also provides users with the option for Speedy meetings. Speedy meetings makes your meetings efficient by getting your on time for your next meeting. As shown below on the screenshot , 30 minute meetings end 5 minutes early, 1 hour meetings end 10 minutes early..