Multiple mailboxes in Microsoft Office 365 may have incorrect or missing time zone settings. This symptom applies to all kinds of mailboxes, such as user mailboxes, resource mailboxes, and equipment mailboxes.
To resolve this issue, bulk change the time zone info for mailboxes in Office 365. To do this, follow these steps:
Connect to Exchange Online by using remote PowerShell. For more info about how to do this, go to the following Microsoft website: