"He is out to lunch now."
Translation:Teď je na obědě.
The corrected version was given as "On je teďka na obědě." The sentence I wrote was "On je teď venku na obědě." Is "ted'ka" a more colloquial form for "now" like "dneska" is for "today"? Is my sentence unacceptable because "venku" need not be included?
Exactly, you understand it right. Dneska and teďka are equally colloquial and venku is not used in this sentence. (However, you can specify "Je teď ve městě na obědě").