For the rest of us that don't follow social media systems closely (just looked up, I'm trusting my search results):

TikTok allows 15 second videos (only 2.5x the length of Vine videos) but also has a way to string multiple videos together for 60 seconds of play time (10x longer than Vine had).

So this is actually a pretty fair comparison (old Twitter @ 140 vs new Twitter @ 280) if you ignore stringing them together.