In case this still needs clarification: Yes, it is theoretically possible to adjust the sun angle at a PhotoField. The only thing preventing it is the "Fixed Camera Only" property, which can easily be toggled in the airport editor.
But altering the sun angle at a PhotoField will only affect the light angle (and whether any glow frames that are present are turned on). It will have no effect on the panorama.
At best, adjusting the sun angle at a PhotoField will cause the lighting on your aircraft and any other 3D objects in the scene to be incorrect compared to the panorama. At worst, if you're actually trying to turn a daytime PhotoField into a nighttime one, you'll have a glowing aircraft with completely messed up lighting against the backdrop of a bright daytime scene. That background is simply a photograph. Changing the sun angle is not going to magically make it look as though it were taken at night.
So, that's why I said earlier that it would not make sense to place the sun anywhere other than exactly where it is located in the panoramic image. It is also why I answered in the negative to the original question, which was not whether the sun angle can be changed at a PhotoField but whether you can change the time of day.
I hope that helps.