In Reply to: I have found it to be true posted by stormy on Thursday, 12. June 2014 at 17:38 Bali Time:
The money changers in Bali run a primitive FOREX operation. They operate as the retail end of the Bank of Indonesia.
When the Bank of Indonesia is shut, the spread between the buy and sell prices widen. When the Bank of Indonesia opens it's doors the spread narrows.
Over the weekend, the money changers reduce their rates, as they do not want to be caught out before the Bank of Indonesia opens it's doors on the Monday.