Sites such as yahoo show historical data for stocks. They show stocks for all different stock markets. When they show information for a day for example the hong kong stock market, are those dates shown at local Hong Kong time? SO for example if I see two stocks on Jan 10th, one is a stock trading on the Hong Kong stock market, and the other is trading on the NYSE, is the Jan 10th of the Hong Kong stock actually a few hours ago before (If I was in living in NY) or is it based on a universal timezone like greentime?
Using your example link, I found the corresponding chart for a stock that trades on London Stock Exchange:
As you can see there, the chart runs from ~8:00am to ~4:30pm, and as I write this post it is only 2:14pm Eastern Time. So clearly this foreign chart is using a foreign time zone. And as you can see from this Wikipedia page, those hours are exactly the London Stock Exchange's hours.
Additionally, the closing price listed above the graph has a timestamp of "11:35AM EST", meaning that the rightmost timestamp in the graph (~4:30pm) is equal to 11:35AM EST. 16:30 - 11:30 = 5 hours = difference between London and New York at this time of year.
So those are two data points showing that Yahoo uses the exchange's native time zone when displaying these charts.