Google Spreadsheet Time Zone Settings
1) Open a spreadsheet, click on "File" menu, then "Spreadsheet Settings...", have a look at the screenshot below:
2) and change your timezone and locale settings, have a look at the screenshot below:
Then click "Save settings".
The changes will propagate to all the collaborators that can edit the spreadsheet.
The timezone affects timestamps, revision history dates, and time-related functions like NOW() or TODAY(), while the local settings change the currency or the way numbers are displayed.