I want to schedule a defrag for every day at 5:30PM. This is on an old Windows XP Pro laptop.

I can never remember what the abbreviations used to denote the names of the weekdays are for the `at' command so here is an example:

at 18:30 /every:M,T,W,Th,F,S,Su c:\windows\system32\defrag.exe c: -v