During recording, DevTest parsers scan requests and responses using a value matching algorithm. The idea is that information on the incoming request can be marshaled from the requests into responses at run time to make responses more lifelike. Similarly, DevTest examines responses for a range of date patterns and attempts to build magic dates that keep the responses from becoming stale over time. Some discussion of magic dates can be found here: Magic Dates - DevTest Solutions - 9.1 - CA Technologies Documentation and magic strings here: Magic Strings - DevTest Solutions - 9.1 - CA Technologies Documentation.
In the lisa.properties file, the lisa.magic.string.min.length and lisa.magic.string.word.boundary help control magic string logic. A little further down in the same file you should see the datechecker properties (regex and formatters) that provide support for different date formats.
Can you provide more information about the actual exception to give some context?
Is the exception occurring inside the VSM or in the consumer application after the response is received?
Do you want to add a date format that is not currently configured?
Are the magic dates being replaced with a value that is not correct?
etc....