Offset start-times in Google Calendar od Christopher X Gerber

Want to start all of your meetings at 5 minutes after the hour by default? That's what this extension can do! It offsets start-times by default when adding a new event in the Google Calendar web UI, using an offset you configure (default 5 minutes). Works with the Speedy Meetings setting in Google Calendar too, so you can leave some room before and after your meeting. Back-to-back meetings are draining; give your attendees time to eat!

Installing: After adding the extension, you need to refresh your Google Calendar page in order for it to work