The easiest way based on what you've got already (and probably the fastest to run) is to create the array array after the "Loop" line (so you know what size it needs to be), then fill it from the collection (and the FileDateTime value), and then sort the array based on the time.

Creating the array will be like this (Variant is safe for String and Date data):
Code:
Dim arrFiles() as Variant
  ReDim arrFiles(1, cFiles.Count) as Variant
Your "rename the files" section will need to be modified to use the array rather than the collection.

The arrays articles in the "Data types/Variables" section of the FAQs will be useful.