Many traders define leverage as a credit line that a broker provides to their client. This isn't exactly true, as leverage does not have the features that are issued together with credit. First of all, when you are trading with leverage you are not expected to pay any credit back. You are simply obliged to close your position, or keep it open before it is closed by the margin call. In other words, there is no particular deadline for settling your leverage boost provided by the broker.
Currencies are traded on the Foreign Exchange market, also known as Forex. This is a decentralized market that spans the globe and is considered the largest by trading volume and the most liquid worldwide. Exchange rates fluctuate continuously due to the ever changing market forces of supply and demand. Forex traders buy a currency pair if they think the exchange rate will rise and sell it if they think the opposite will happen. The Forex market remains open around the world for 24 hours a day with the exception of weekends.