Enter TwitterSpirit and Efemr, which enable users to schedule their tweets for automatic deletion after a specified period of time using hashtags like #1m, #2h or #3d. According to Wired, using these services will (in some cases) also delete retweets. That said, tweets with #time hashtags can always be copied manually in any number of ways, so the self-destruction is not total. Nevertheless, their visibility can still be reduced by using TwitterSpirit and Efemr. Lastly, the use of these hashtags also sends a social signal that these tweets are intended to have limited temporal use.
Note: My fellow PopTech and Rockefeller Foundation Fellows and I have been thinking of related solutions, which we plan to blog about shortly. Hence my interest in Spirit & Efemr, which I stumbled upon by chance just now.