There usually aren’t sufficient foreign currency cashflows over the weekend to induce large fluctuations in the exchange rate when Monday comes around, so it may be better to wait for the open of the markets on Monday. No, exchange rates do not change daily, in the sense that the exchange rate does not change just once a day. For example, the pound will not change value just once versus the euro or US dollar, from Monday to Tuesday. The reason why the exchange rate seems similar at the open on Monday is because moves usually become insignificant towards the end of Friday, which is one reason to avoid trading on that specific day. In fact, more than a year ago I did a very stupid trade in going against the trend on the GBPUSD.