I thought something like this might work:
You could have four layers ( 1 each for summer and winter in each hemisphere )
For summer down under:
Assuming summer starts 1 Dec and ends at end of February ( I am in Australia and that is how we do it )
Winter "up north" would be the same as above but days would be adjusted to be the day equivalent of the solstices and the hours of sunshine would be less than 12
And similar for the other pair of summer/winter layers.
It is of course very simplistic and ignores leap years. I suppose one could create a more complicated expression to address that.
As one approaches the equator it might become more interesting
Anyway, as a crude approximation, do you think the above might work?