I am not sure whether others need this or not (it is useful for my use case), but I have released a node (among others) to convert DateAndTimeValue columns to DoubleValue columns and back. It supports offset and scaling.
The documentation is available here: http://eureqa.ivi.eu.com/documentation/date-converter
The update site is here: http://eureqa.ivi.eu.com/file-cabinet/20110701
Home page: http://eureqa.ivi.eu.com