In principle time-varying shade could be encoded based on azimuth and altitude of the sun, e.g. 80-70:30-50,316-90:0-45, could indicate that (in the southern hemisphere) there is shade when the sun is from 80 to 70 degrees between the altitudes of 30-50 degrees, and then from 316 degrees until 90 degrees (overnight) as long as the altitude is below 45 degrees.

This could perhaps be combined with percentages in a manner similar to conditional rules, e.g. yes @ 80-70:30-50, 316-90:0-45 ; 70 @ 80-70:50-70; no @ 100-90:45-90 i.e. in addition to total shade, the way is 70% shaded if the altitude is between 50 and 70 degrees for the azimuth from 80 to 70 degrees, and there’s no shade in the morning (azimuth 100 degrees to 90 degrees) if the sun is higher than 45 degrees.

Tools would be needed to enter or produce this type of data, and there’s still a problem of how much precision to enter. It wouldn’t be too hard to enter individual points, e.g. yes @ 80:30,70:50 by having a user indicate that shade is present at a particular time, for which the sun position can be calculated. The question is then how to convert point data into a set of complete ranges.