Dynamic Shading Value?

Is there any way to update the shading value by date?

For around 8-9 months of the year my shading is 0. However for about 6-7 weeks either side of the shortest day (22 June here in NZ) I get shading (From a single Totara tree in the paddock next to my panels) till around mid-day. e.g.

is there a handy script anywhere to dynamically update the shading value based on date?

Its a fixed value that applies to the whole day in the estimation.

Yes it’s fixed… But I’d like to make it dynamic on mine because it varies based on the time of year.