There are two things to do with the import servlet:
Importing data using existing importers is done using the API, as explained in HTTP API (import module).
A collection of details about the importer
While the date formats of both iCal and vCard are pretty clear, csv can be defined freely (insert "of course" or "sadly" as you like).
Microsoft Outlook does as it likes:
Our own format uses the timestamp format. Advantage: You can use hours and minutes. Disadvantage: You'll have to use negative numbers for dates before 1-1-1970.
Information for developers: The date format interpreters are build to be exchangeable, you can use your own format there.
Adding a new importer is explained in Building an importer.
See also: Using the export servlet.