Haven't you see any scifi/action shows? It takes at least 5 minutes to activate the self destruct, OBVIOUSLY
In all seriousness, this has been bounced around before, and turned down for a combination of reasons. AI would freak out, pretty difficult to code, and it's really not worth it.
The scuttle button does however, work against the flood - the timer keeps going after you lose control and the AI doesn't know how to handle it.
Really? I'll have to test this out. Ready the test subjects!