Solr expects dates to be in UTC when indexing (except [wiki:ExtractingRequestHandler Solr Cell], which has some leeway on transforming dates from various formats). Specifically, from the Example schmea.xml, the comment says:

The format for this date field is of the form 1995-12-31T23:59:59Z, and is a more restricted form of the canonical representation of dateTime http://www.w3.org/TR/xmlschema-2/#dateTime The trailing "Z" designates UTC time and is mandatory. Optional fractional seconds are allowed: 1995-12-31T23:59:59.999Z All other components are mandatory.

Expressions can also be used to denote calculations that should be performed relative to "NOW" to determine the value, ie...