"My computer is never on at 0100 on any day so when, if ever, does it defrag?"
Go to "Computer" -> right-click your C: drive -> Properties -> "Tools" tab -> "Defragmentation" button. Look in the "Current Status" section and you'll probably find that the defragmenter has actually been run when the PC was switched on and the drives are 0% fragmented - like this. In the unlikely event that things don't look that way then click the "Configure Schedule" button and modify the time and day to your liking.
Alan, if you mean the Task Scheduler then that's an overly complicated way of changing the defrag settings. It's much easier to use the "Configure Schedule" button I mentioned which does exactly the same job.