Green Sky?

NewEarth has some interesting features as a planet. It has twin suns and two moons. The days are considerably longer, 36 hours by earth time and each cycle or year is 450-451 days. The sky has a definite greenish cast and it rarely gets completely dark because of the light of the two suns and reflected light of the two moons, only for a few days during the coldest and warmest seasons does it become completely dark. In an effort to keep track of time, when the humans arrived, they did use a sun dial to gage time, but hours based on shadows were confusing because of the twin suns. Can you tell what method they are using?