I think we're entering in details here. We're talking spam (99.9%) that has been sitting there for 3 months. Seems there are little objections to the deletion of those messages, great. Some suggestions for how to record that action - I guess it is up to the admins whether that is suitable and worth the effort (I dont'see an upside, but if it is very easy, why not).
I do think 2 weeks would be much too short - lets stick to the term where it's obvious (3 months), and we can re-evaluate later if it should be shorter.
Best,
Lodewijk