Dates are treated no differently to text with no specific semantic meaning.

There is no semantic element in DITA for dates in the flow of text in content, and they are therefore simply typed into the content.

You should, however, use consistent and standard notations for dates. Dates are represented numerically in different ways in different cultures, even within the same language group. Interational Standard ISO 8601 specifies rules for the numeric representation of dates; you should follow these standards where possible.