Those who have given up on the Viking Settlement as "impossible to complete within the deadline" have probably stopped reading this thread, but in case some of you still are reading it: I thought the same thing as you the first time. But after going through it a few times, and reading the advice given here in these forums, I can honestly say, it most definitely IS possible!
I play in two worlds, and the first time through, I just barely got the "gold" reward chest in one world, and got the silver in the other. And the only reason I got the gold in one was because I had a lucky arrangement of rocks, *and* got a well-timed 4x payout. The second time through, I didn't get so lucky and got the silver chest in both worlds. Then I read the advice on these forums and tried to follow it. And the third time through, I got the gold chest in both worlds - one of which had an absolutely HORRIBLE arrangement of rocks - taking a big bite out of the middle of the side of my starting area. And I still got the gold, with a good amount of time to spare - and I didn't even follow the advice exactly. Now I'm going through for the fourth time, and I expect I'll always get the gold every time from now on.