Hold out your arm with your hand at a 90 degree angle to your arm so that your hand is between the bottom of the sun and the top of the horizon. Be sure to squint (almost close your eyes), so that the sun doesn’t hurt your eyes.
How many of your fingers ‘fit’ in that space (bottom of sun-top of horizon)?
That is the time.
Four fingers is usually about 1 hour before sunset.
Q) I have short arms and stout fingers? Won’t my ‘finger time’ be different than someone with long arms and skinny fingers?
Okay, these directions are for the people who think they //really// need to know the answer:
How many of your fingers ‘fit’ in that space (bottom of sun-top of horizon)? You might discover that only 3 fingers fit…or that you have to use TWO HANDS to stack enough fingers up to fill the space!
Now do a little clock watching to see how many minutes it takes for the sun to actually get down to the horizon. Divide the minutes by the number of fingers that fit: now you know how many minutes your fingers are worth!
Be aware that your ‘minutes per finger’ will vary according to the time of year, location on the planet, and your view of the horizon.
Second answer for everybody else:
It doesn’t really matter. When you see the sun getting close to the horizon, go find the party!