It is possible to set in HT on what date the exchange rate will be selected for the conversion of documents with the dual currency template ( for items on invoice, total and payment).
It is possible to choose from 3 options:
a) Valid at time of print = the exchange rate valid at the date and time the document was printed is used for conversion. If the hotel rate changes daily, the conversion will be different every day
b) Tax effective date = the exchange rate that was valid for the Tax effective date will be used.
c) Creating a document = the exchange rate valid on the date and time it was created is used for conversion.
The default setting is "Valid at time of print".
The settings can be found via Settings - Application - Main system set-up - Miscellaneous settings tab.