Dynamic light affecting environment billboards depending on the angle of the light looks bad

Hello, I am developing a game in which remote areas, cities, mountains and forests are “billboards” (but they don’t look at the camera). They are quads on the scene with a material.

The problem is that I want to make an upgrade and put cycles of day and night. What makes the billboards have light or not depending on the angle of the sun, that is, to the angle some have a lot of light and others nothing. It looks pretty bad. As you can see in the images.

I tried using standard material but it doesnt look good because of what I said earlier.

Do you know any workaround or a way that billboards are affected by the dynamic light as well as the floor? Thank you so much in advance.

Standard material daytime.

Standard material nightime.

Disable lighting from the billboards and adjust their “color tint” by the time of the day, eg. on night they are very dark blue, on midday yellowish white, on sunset deep amber etc.
It will require some tweaking to match the billboard colors to current light color.
It is also advices to adjust the ambient tint according to the time of day.