I could not open your VI as I do not have version 6.1 installed. So here are some comments...
You can build a 1-D array of time steps by using a for loop, delta T (the inverse of the ACTUAL scan rate as indicated from the acquire VI), and the number of points (use the Array Size function on one of the data columns).
Now, since the DAQ VIs output in column major order, first transpose the DAQ record and then use the bulid array fuction to add the new row to the first position.
Transpose the new array back to column orientation and write to spreadsheet file.