you are right and this is the way it works. For me it is a massive improvement how it works with Fuji and longtime exposure. Coming from Nikon (and what I have heard other brands have similar behaviour) where I always have the to carry and intervalometer or at least a remote release with lock, this is much easier. As you mentioned, there is always the possibility to end the long exposure before the end of the timer.
PS: Yes, I know the the "time mode" with the Nikon. 😉