How do you change SharePoint Online to use your local time zone? :If you upload your documents only to find that your Modified time stamp is hours off, your SharePoint Online site may be using the wrong Regional Setting for your Time Zone. This is generally set to Pacific Time (US and Canada) by default," a Office 365 Technical Blog member.
Here are the steps to correct it:
- In your team site, click Site Actions.
- Click Site Settings.
- On the Site Settings page, under the Site Administration section, click Regional settings.
- In the Time Zone section set the Time zone drop-down list to the appropriate zone for you.
- Click OK.
Check the Modified time stamps of your documents, or upload something new to be certain the time is reflected correctly.
Watch the video walks you through these steps:
[Source:Office 365 Technical Blog]