Action Details
Requirements and how-to articles for Google My Business's action:

Write a post about an event your business is hosting. Unlike other post types, event posts do not expire after 7 days and remain live until the event is over.

You need this to get it done:

Event Title
The name of your event.
Write about your event (maximum of 1500 characters.)
Start/End Dates and Times
Set the start date and time and the end date and time for your event.
Photos should be simple, direct, in-focus and well-lit, with bright, vibrant colours.
File format: .jpg/.png
Minimum resolution: 400 x 300 pixels
Note: You can use either a photo or a video, but not both.
File format: .avi/.mp4/.mov/.flv/.wmv/.mpg/.m4v/.mkv/.m2ts/.mts
Maximum file size: 100MB
Note: You can use either a video or a photo, but not both.
Call-to-Action Button
The following calls-to-action are available with event posts: "Book", "Order online", "Buy", "Learn more", "Sign up" and "Get offer"
Requirements missing or found errors? Report

How-To Articles
A list of useful links for you:

Google My Business Help - Post on Google
Official guide to making business posts on Google.
Link missing here or found errors? Improve How-Tos