'at' command syntax

[Drew Tomlinson]

I'm am unable to figure out the proper syntax of the 'at' command.  I've 
read the man page over and over.  I've attempted Google searches but 
there is a lot of  'at' in the world.  Can someone please point out 
what's wrong with this syntax?

at noon '/usr/local/bin/curl -u user:pass -d status="New products added 
to catalog. Check out the demo videos! - http://bit.ly/7dtLny" 
https://twitter.com/statuses/update.xml'

I've tried various ways of specifying time but always get "at: 
incomplete time".  However if I just enter 'at noon', then I am in an 
interactive mode where I can paste the command, end with ctrl-D, and my 
job gets scheduled.  What am I missing?

Thanks,

Drew