This is a feature you would use, if you are using a fixed conversion rate for your currencies.
You have the option of adding you own fixed currency exchange rate and to add various date ranges to your fixed currency exchange rates. E.g. you are using one conversion rate 1st of January - 1st of June. Then you would like to have a different exchange rate from the 1st of June and onward.
To add a fixed exchange rate start by selecting "products" on the top bar and "Pricing" from the drop down list.
Select "Actions" and "Currency settings" from the drop down list.
Select "Add currency setting" to create a new fixed currency exchange rule.
Fill in the form to define the parameters for the currency exchange rate
Save and remember to publish your price catalogue to activate the new currency exchange rate.