Nobody should build a boat outdoors. Do what I say, not what I do, or have done.
As in the picture, and its not really a boat, just built like one, notice the bog is dark. I use the slowest hardner in hot weather, but add graphite powder to make it dark grey or even black. That enhances a solar cure so I can be sure it will be sandable the next day. That also helps on cold days with a heat lamp.
Notice how the bog bits get darker as I get closer to completion.