Das Museum wurde vier Jahre lang umgebaut.
I have these two possible translations, but I am not sure, which is correct:
- The museum was rebuilt four years ago.
- The museum has been rebuilt since four years ago (and is still being rebuilt).
You don't have any information when the museum was rebuild. You just know that work is finished, but you don't know if they finished yesterday or 350 years ago.
Here you don't have any information how long it took to rebuild the museum. But you can guess that it took less than one year. Because if it did last longer, you would say something like.
Here you just know when they started and you know that they still work. But you don't know how long it will take and when they will be finished.
Note, that in German you use present tense (because they work now).
Das Museum wurde 4 Jahre lang umgebaut -- it took 4 years to remodel the museum.
Eine Angabe mit "lang" ist ein Zeitraum, kein Zeitpunkt (wie es Dein Beispiel (1) nahelegt). Da würde man statt dessen z.B. "Das Museum wurde vor 4 Jahren umgebaut" sagen.