Google has told that any google posts which has not been updated for more than a week can be removed from the site. It requires constant update to keep your posts posted on the google site and receive fresh messages in local panel.
For the posts which are related to an upcoming events have a exception in this case. Posts related to events get removed only after the date of the event. Otherwise all other posts get removed if it don’t get updated for every 7 days.
The customers of Google my Business has to keep in mind about this information as the Google post has went live to Google my Business customers recently.
A Google spokesperson said, Posts enable merchants to share timely, relevant updates on Google Search and Maps. To ensure that posts are timely, they’re removed from the default view after seven days (or when the event date the post referenced has passed). However, a historical view of posts is shown under the Posts tab on mobile.
Even though google spokesperson has told about it , Google Posts help documents has no information about this google post expiration yet.