First, the data would have to be in Mathematica's syntax:
my data = { {{2014,1,1}, 2.50}, {{2014,1,2}, 2.51}... etc }
This can be plotted with DateListPlot, but ...
the function Interpolation won't take that date specification however, so we have to convert it to a simple number. There's a number of ways to do this.
One way is to apply AbsoluteTime to the list which represents the date.
If you're new to programming with Mathematica, take a look at the Virtual Book for an introduction:
http://reference.wolfram.com/mathematica/howto/UseTheVirtualBook.html
