In the beginning of Stave 2, after Marley's ghost has disappeared, Scrooge wakes up believing he has overslept and that the time at which the first ghost was to appear has passed. To confirm this, he looks out the window only to find out that it isn't morning yet.
The following follows:
This was a great relief, because “Three days after sight of this First of Exchange pay to Mr. Ebenezer Scrooge or his order,” and so forth, would have become a mere United States security, if there were no days to count by.
What does this sentence mean? More specifically, I can't interpret these 2 parts:
"Three days after sight of this First of Exchange pay to Mr. Ebenezer Scrooge or his order", and
"would have become a mere United States security, if there were no days to count by"