Thanks Jerro, I went ahead and used a pointer reference to ensure it's being saved back into the array (http://dpaste.dzfl.pl/52710926). Two things:
1) still showing zero time delta
2) On windows 7 x74, using a SAMPLE_AT size of 30000 or higher will cause the program to immediately quit with no output at all. Even the first statement of writeln in the constructor doesn't execute.