Daily candles usually go from midnight to midnight. In most charts, if you hover over a candle, there will be display somewhere on the chart that tells you the timespan of the candle.
I know that it's midnight to midnight. The question is which time zone different exchanges or data providers use for their charts. TradingView, for example, uses UTC time as their default time zone, so I assume that a new daily candle forms at midnight UTC (London, UK). But could different exchanges perhaps use different time zones for their daily candles, or do they all use UTC? If not, then daily charts would look different on different platforms.
EDIT: I now checked both GDAX and TradingView, and they both produced a new candle at midnight UTC (4 PM PST). So hopefully this means that everyone is doing the same thing. Which, of course, would make sense.
