Question about Outlook Express

Here's the scenario: I have two Exchange accounts set up on my Outlook for Mac 2011. I'd like to keep one of the accounts online but turn the other one off-line for a few hours - maybe until 5pm. I have seen one account online and the other offline in cases where for some reason the server connection could not be established but how do I purposefully take one of the accounts off-line?

Thanks for your help!