Case 1 sounds basically like a homework inbox. I can see that as being useful, although I’m not sure timed replies is how I’d go about it. Wouldn’t it be better to just have a feautue that’s specifically for this, rather than asking everyone to set the same time (and possibily getting it wrong)? I would suggest topic timer that keeps all replies hidden until the given time, at which point they are revealed.
Case 2 sounds like the existing timed topic feature should usually work.