Setting the time zone for all SharePoint sites in your tenant
The default time zone for any sites created in SharePoint is US Pacific Standard Time (PST). For users who aren’t based in this part of the world, it can cause issues in terms of date columns in SharePoint, including the Modified and Created dates. This is why one of the best things you can do when embarking on a SharePoint project is to fix the default time zone for all SharePoint sites.
When creating new sites from the SharePoint Admin Center, you do have the option to change the time zone one site at a time in the site details panel under “Advanced Settings”:
However, it can often be missed and means your site will default to PST time.
So to avoid needing to manually change this for each site, you can change it at a Global level.
To do this, go to the SharePoint Admin Center, Click on Settings and the Site Creation. You can then select the correct time zone for your organisation and click Save.
Just note that changing this setting only applies to future sites. Any sites created before this Global change will still have the PST time zone.