Yeah, @mlucas, I figured this was an optionlock after I posted it. It was weird how it just snapped into comprehension. Though, I think it can be dangerous to draw too many conclusions from single-sentence stories.
I'd say e) is definitely not a timelock -- it's not fixed in time, and their actions extend it. (sometimes, this is how I think about it: nobody can adjust a timelock, but people's actions bring out the climax of an optionlock)
f) I'd say it should have been an optionlock -- they should have sent the bomb into the sun! -- but if they know it's coming back in 50 years, that sets a timelock.
BTW, I don't think it's necessarily bad to jerk an audience around, you just have to be consistent.
Nah, because the limit brings about the climax. In this case, the timer going down does this. It forces them to make a choice, but the limit isn't about that. It's about what forces the choice.