When created a new SQLObject class, you can define fields to have a default content of a time-stamp.  Simply reference (if you are using MySQL) the NOW() function, using the FUNC keyword.  Here's an example::
 
    class License(SQLObject):
        client = ForeignCol('Client')
        signDate = DateCol(default = sqlbuilder.func.NOW())
        expiresAt = DateCol(default = 'signDate' + '1 year')