The portfolios will now show you the overall change from the previous day. For each portfolio you can choose a timezone that best reflects the exchanges the stocks are listed on. After the market has closed in that timezone, we snapshot the value of your portfolios to calculate against throughout the following day.
Existing portfolio timezones have been set based on what exchanges feature in a portfolio, defaulting to America/New_York.
The portfolio panel on the new home page has also been updated to show this change.