How To Determine Daily OHLC prices for BTC/USD

Hello,

How do I determine the daily OHLC prices for BTCUSD? It trades 24 hours a day so does this mean open price is determined at 0:00 time?

Thank you

yes but the problem is what time zone?

i meant, according to what timezone is the daily candle determined? hope someone knows. would be good to know also what website offers correct charts (if there is any). i have compared a few and the candles are not the same.