{datetime} is about either setting time stamps for your document or handling time data in {diagrams} (e.g., using {pgfplots}). If you are setting the date/time for a title, include the {titles} tag.
datetimeis about either setting time stamps for your document or handling time data in diagrams. The former typically involves the \date "field" being set to \today for titles, but could also refer to setting time-related PDF properties.
Common packages associated with date formatting include isodate and datetime.
isodateallows for various formatting of language-specific dates. The command \cleanlookdateon removes the ordinal numbering of the day and simply prints it as a numeric:
\documentclass{article}
\usepackage[UKenglish]{babel}% http://ctan.org/pkg/babel
\usepackage[UKenglish]{isodate}% http://ctan.org/pkg/isodate
\begin{document}
Original date format: \today \par
\cleanlookdateon% Remove ordinal day reference
Modified date format: \today
\end{document}
A popular package for diagrams/plots involving time data is pgfplots.
