Time Frame for Daily GBP/USD

Hi All,

I’m looking at daily charts for currencies and they have a daily pen/close price. For currencies what is the opening and closing time that those charts refer to? I’m using charts on IG Index. I’m looking to trade using daily charts once I learn a bit more, but unsure as to what time of the day they refer to. is it 8am - 17:00pm GMT?

Many Thanks.