Python. IMO, it's so well designed that you can gain a comfortable (albeit still beginner) grasp on it within 40 hours, especially if you have prior programming experience.
There are many many IT skills you could learn in 40 hours. Assuming you are not a complete n00b, how about learning Ruby and Sinatra (a "framework" for rapidly creating web applications). You could easily make it through the book, "Jump Start Sinatra," in less than 40 hours, for example.
Is this the type of response you're looking for? If not, please clarify. Good luck!
My wife and kids are away for a week in the near future, so I thought I would take 40 hours and learn something new. I have no idea yet as to what that will be, so I thought I would ask more intelligent people what they would do :)
Metrics measurement and tracking of some sort, depending on your area of interest and existing expertise. That could be Graphite and statsd, or a particular type of web analytics like Google Analytics or MixPanel. It takes roughly 40 hours to get a good basic understanding, implement, test, and start tracking useful things with each of those.
I'd go with NoSQL (any of them, overview of all of them?) or AWS/cloud stuff, because I'm already familiar with Linux administration and RoR. In the enterprise you don't get to work with that sort of technology, so that's where I'd spend my time.
