This level is a piece of cake, and only the last part matters timewise since the beginning part until Custer's Scouts arrive has a fixed timespan. In this fixed timespan it's very important though to destroy the 6 buildings along the scouts path before they arrive, otherwise the scouts will have a very long pause (I'm not sure how much exactly, but it's at least a minute, probably much longer) at each of those buildings until they move on. But if you've destroyed all 6 buildings, the scouts will move on immediately without pausing which saves a lot of time (And units, since there won't be extra enemy units at the end of the level). I also use a Flaconet to destroy one of the buildings. Quick, easy and efficient. Well, after those 6 buildings are destroyed, I need to wait, for a very long time :D So in the meantime I get some more units, and also some more Settlers to fill my Fire Pit to the max so that the Fire Pit can provide maximum unit damage for the end fight. When the pass opens up, I destroy Custer's Scouts because otherwise they'll follow me to the top while killing my units, which isn't very useful. When Custer and I clash together, the rest of his army will scriptedly continue walking to my town at the bottom... Doh! ;)