I came across this handy tip over at Lifehacker website. I think that’s pretty useful for outdoor photography, when camera people want to some of the best sky colors.
All you need to do is extend the hand full and count the number of finger width distances between the sun and the horizon. Each finger is approximately 15 minutes, which means each hand is about an hour. This is of course just an approximation, but it’s always better to have an approximation than nothing at all. Enjoy.