A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hi Beth,
SharePoint on-prem uses your local time zone and SharePoint online uses its own time zone. When you migrate SP2013 to Office 365, it changes the Date Time value (in your local time zone) to O365 time zone and that’s the reason dates are off by one day.
In this case, you must check the regional settings for the affected site in SharePoint online.
For your reference: Change regional settings for a site
Thanks,
Neha