Quite well thought out, except that it's not "at your leisure". You can only look 30 seconds back.
If you got hit by a vehicle, you'd probably be too dazed/shocked to use it. Similarly if you were mugged. You'd need to be looking into the past at the latest 30 seconds after he left your field of view, and that would only give you a single instant of viewing before it started showing you the time when he was already gone.
Sure, it would work if you had an eidetic memory, but if that's the case, you don't need it anyway.
EDIT: Also, sorry, I didn't realize this was Wonder Square. I thought it was General Chat, which is why I was treating it more as a general discussion than a "game".
I am really, really not good at the "thinking new ones up" part, though, so I'm just going to point out that Yerushalmi solved one without putting up a new one, and head on out.