When it’s late afternoon and you’re wondering if you should make camp or not, use this trick for estimating the time until sundown.
Extend your arm and your fingers toward the sun, then bend your wrist. Each finger represents about 15 minutes.
Leapfrog your other hand if needed to estimate times more than 1 hour.
Note that this thick works if the horizon is flat or a mountain ridge line, it doesn't matter.