I did a little calculation for my axe production. Next Building i can unlock will be the clan shrine and i still have 13 days left. And i never used diamonds.
It costs me a total of 327 axes from now on to research all buildings. (thats different for everyone I know but for me axes are the bottleneck)
Divide the 327 with 5 = 65,4. So i will need 66 times the 4h production to finish my settlement. Thats 11 days if i can be online every 4 hours. I guess it is possible to use one 8h production a day with my coin production. So its possible to go to sleep or work 8 hours
So 11 days is nearly the optimum for me (without the 3% multiplicator). Of course i can build another axe smith, but then another production will be my limit.
I would say it is possible to do it in time. But with a lot of effort. Maybe a little to much. And what i think is funny when someone is saying that an inno member was doing it in 15 days on a speedserver. Yes of course i would manage that as well if I had one day of playtesting without the waiting 4h every time. It is not that it is very complicated but difficult to be online every 4 hours for 21 days....
At all i like the event and the chellange, but i think it needs a little more finetuning. and the luck factor is very high. When I get 4 times the goods thats nearly one day less but with a chance of 3%... I am not sure how fair this is.