Thanks for posting your request! Opening 3D models in BIMx according to the exact date and time defined in Archicad would be practical indeed. We first targeted visual quality and have already started assessing the needs for shadows' future improvements.
Could you please describe in detail how you would like to change the sun position by date and time in BIMx?
I encourage others to answer this question and discuss the topic.
I am currently working on a feasibility study which is very much dependent on sun studies. I would like to be able to export multiple 3D views, each with a different date and time defined as per the views saved in our model. In other words, can the 3D view in the BIMx have the same date and time settings as the 3D view in the file?
Also, we generally recommend exporting camera positions for BIMx's Gallery instead of multiple identical 3D models. You can already present the model with different sun positions by aligning the sun in BIMx (with the help of Archicad) and saving Favorite views. This article describes how Favorites and Gallery work, I hope it helps.