I’m generally less concerned with what the time actually is and more often interested in how much daylight remains. Whether I’m out on the trail preparing meals, collecting firewood, or setting up camp, I prefer doing so while the sun is out. I’ve also found this helpeful on motorcycle rides and during photoshoots.
First, use something to block the Sun, like your other hand or a tree, because looking directly into the Sun is a bad idea. Next, with one hand, measure the distance of the bottom of the Sun to the horizon. Each finger between the Sun and the horizon represents about 15 minutes. If you add them together, you can approximate the amount of daylight left.
Illustration credit to Show Me How To Survive by Joseph Pred
Furthermore, if you’re aware of the typical time of sunset, you can subtract the approximate amount of daylight left to discern the approximate time of day.
The caveat is that this technique is latitude and season specific. To clarify, the Sun will have a shallower viewing angle the further North of the equator you are. The Sun will appear to set faster depending on geographical location. Nevermind Earth’s atmosphere causing an optical distortion, or the Ponzo Illusion. Thinking about it, that didn’t really clarify any stipulations at all.
Essentially, remember that these are not precise methods of time measurement, and the margin for error will vary depending on where you are.