I don't see the Force in @AbdulAlhazred's scenario.How much Force can be applied before we stop being able to call it Story Now and move to Story Before?
To elaborate: suppose that the space station is doomed because its reactor is melting down. And suppose on of the (Traveller) PCs has Engineering-4. Well, that PC clearly - by the game rules - has the technical skill and knowledge to hand failing reactors. And so the only way to ensure the doom would be to block/veto attempts to repair the reactor. That would be force, absolutely.
But suppose that none of the PCs has Engineering skill? Maybe it's a group of Rogues and Diplomats who have been stranded there.
Or suppose that the doom is due to failing food or fuel supplies - Traveller has no player-side mechanic to try and make such supplies available, so if the GM decides, as part of establishing backstory and subsequent framing, that no supplies are coming, then that's that. No force is needed to maintain those elements of the fiction.
That was why, in my 4e example, I contrasted Heroic tier PCs - who have no abilities to do anything about the Dusk War - and Epic tier PCs, who do.
I don't know what the source of doom was in the space station scenario, but I can easily see it being there without requiring any force. Just backstory and framing.
As to the question of how much of the fiction needs to be up for grabs if it is to be story now and not story before, I think there's no concrete answer here. It's certainly not about quantity (if that even makes sense) nor about content in the abstract. It's more about the capacity of the players to exercise protagonism in relation to the thematically salient fiction. In some RPGs and some scenarios that will be tightly focused, in others it will be more open-ended.
Another example I just thought of would be an Arthurian RPG where the core legend is pre-scripted (maybe like the Great Pendragon Campaign? I know of it but have never actually looked at it). There obviously are approaches to that which would be Right to Dream and not story now, and I think Pendragon by default probably encourages such approaches.
But in a game in which we all know that Arthur and Mordred will have a confrontation at a certain time and place, with a certain consequence, there could still be story now play. What choice does the player make for their PC? What alliances do they try and forge? Whom do they betray? And of course the GM has to make certain choices, like not allowing the PCs and Mordred into the same scene, if that means the former getting a chance to kill the latter. That's relatively pro-active scene-framing, but needn't vitiate story-now play. I could imagine myself getting into the game I've just described fairly easily.