Does this mean literally "down," or is this a colloquial thing? I.e. "I am available at noon."
Yes, this mean literally "down". For example: "I am down (in the park) at noon."="Lent vagyok (a parkban) délben." So "lent" is not only means "available". "I am available" rather means "én elérhető vagyok" where I am=én vagyok and available=elérhető.
I'm down at noon doesn't mean anything. When would this sentence be used in English, or Spanish for example? "Estoy bajo en mediodia". Down where???
Downstairs, down in the city, down at the docks, down in the cellar. There are many ways you can use "down". Needs some context, though. :)
But if you want to use it context-free, you can go with "downstairs". That's a possible translation of lent, too.
I purposely wrote "At noon i am downstairs" It was marked right:-) So this is goood.