Thank goodness for the 'at' command, and for this writeup which helped jog my memory and allow me some beauty sleep.
So, 4 hours of 15 second interval of iostat starting at 12:30 am on April 12? No problem. And sasquatch beauty sleep abounds!
echo "nohup iostat -DlRT 15 960 > /home/sasquatch/temp/iostat_20130415.out" | at 0030 April 12