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')