The carry trading is a strategy in which an investor sells a certain currency with a relatively low interest rate and buy another currency with a higher interest rate. The aim of this strategy is to get as profit the difference between the two interest rates, a benefit that may become attractive depending on the amount of leverage used. As the profit comes from the interest rate differential, you can make a profit even if the price of the currency does not change a single pip.
Although the Forex market operates 24 hours, is taken by consensus UTC 0 hours as the end and beginning of a new trading day. In Forex trading, at the end of each day is credited or charged to the account of the trader the spread between the interest rates of the two currencies of the currency pair in which the trader have open positions at this time (this is known as Rollover).