I revisited this map in HoTA in tournament mode. I think 14 days is the absolute minimum that it can be beaten in (and it took me a number of tries to cut it down to that). Effectively, you need expert logistic at the end of day 1, advanced pathfinding by the time you get overground and expert navigation to cut the duration of the sea voyage down to 1 day. Expert logistics allows you to skip conquering the first town and proceed directly to the second one... and so on...