Currency conversion is available between 7am (GMT+8) and 6pm (GMT+8) every working day, except for currency holidays.
A currency holiday is a day in which there is no conversion available for the selected currency or USD. This is because, to successfully convert currency, it must be a business day in the countries of the buy and sell currencies, as well as in the US. You can find a list of the currency holidays for 2022 here:
Currency holidays 2022