[ZhL]

That's what I thought, only most recent timeline counts. From my experience anything older than 15-30 minutes is not noticed anymore. So I agree, that's a good amount of time to use as the grace period. Just intuitively I think people wouldn't care to remove their retweets. I might be wrong though. Need to get more data on this. I read Twitter ToS pretty carefully, and I didn't find anything that my service would violate. As for Apple, still need to look into that.. It is something I see all the time though. And I do it for my own apps without any issues so far.