Only 4 years of work to be ready? That sounds pretty optimistic (crying in German)
Norway's rock are not bad to dig in. The rock is hard but we know how to work with it and that same hard means you don't have the safety problems of a collapsing roof to worry about while digging.
Reading the Wikipedia page (including the originally projected end date of 2026), it sounds a bit worse. Probably not Germany bad, but I wouldn't bet on the 4 years either.
Ask a Norwegian to dig a tunnel and they will turn into a gopher on meth. We are the undisputed champions of tunnels in terms of tunnel density. Show us a piece of rock and we'll put a big hole in it.
However.
Ask a Norwegian to fix a piece of road and you will be staring at a hole in the ground for 4 years while people will take turns leaning on a shovel in that hole while surrounded by at least 4 different categories of supervisor or inspector.
But to inject some realism: if they say 4 years they can probably do it in 5. And it'll take another year or so to fix fuck-ups that in retrospect will look stupid and thoughtless, but which are realistically unavoidable. We'll whine about it. A lot. And each week the whole country will be experts on something new. Like evil-sounding compounds for stopping water ingress or how to insulate wires. And then suddenly it starts working.