As an aside, I recall a reference to "speed of plot" from any number of scifi authors especially for TV when questions of how fast the ships move. I recall also the use of one lampooning of this by having one helmsman answer "how far away at top speed?" with "two commercial breaks, sir."Exactly - it either happens (in means and ways either expected or unexpected) or it doesn't.
Forcing it to happen via arbitrary decisions made by you-as-DM is in my eyes just another form of railroading: you're not being neutral, nor are you presenting the setting and events therein in a neutral manner. Instead you're tweaking these things in response to what the PCs do, in order to force drama upon them - drama which the PCs might prefer to avoid, mitigate, or pre-shape if they had the ways and means to do so that you have denied them.
Followed by the drama of whatever happens when the enemy force thunders in across the drawbridge...
Cool - though in my view geography in particular is something that absolutely has to be fixed* in place, and properly so.
* - unless one is in a dreamworld or similar where these things are not constant
I ran into this when reading through a published module the other day (forget which one now) where the very pretty maps had obviously been scaled to suit the specific goals of the adventure designer in different parts of the adventure...resulting in two specific locations being x distance apart on one map and y distance apart on another, according to the scales on the maps - where x and y differ by a factor of about 4.
Obviously the adventure designer wanted travel time between these two sites to be short when dealing with local stuff but much longer when dealing with regional travel.
As a trained geographer, I see this as abhorrent!
A trope and structure that likely fits some styles fine and others not well at all. Just like say "coincidence is fine to get heroes into trouble, but not out."