Well, I don't what you tried with "arrays", but it should work just fine. Since you have a time axis, I assume you want an XY graph.
The attached simple example shows one possible solution (LabVIEW 7.1). Instead of reading the spreadsheet files, I read from string constants, but the rest should behave the same. Just substitute your File I/O in the event structure.
There are many ways to do this so you would need to adapt it to your exact requirements.