Hello Sébastien,
there are a few things that come to mind:
– usually buildings in architectural visualisations have perfectly straight vertical edges, like in architectural photograpgy (I’m not sure how to correct the camera in Blender, but you can do it in Photoshop at the end, or maybe there is a plugin)
– it appears that the sunlight is coming from behind the camera, but the sky shows the sun rising behind the building
– the lighting is very important for setting the morning mood, with a warm orangy light from the sun and interior lights and cold purpleish shadows, here are some examples that maybe can help you. Also I believe low fog to be important for the morning mood.
https://www.ronenbekerman.com/showcase/sunny-morning-by-nouvelle-mesure/
https://www.flickr.com/photos/125701341@N07/22204958422/
https://www.behance.net/gallery/50710989/Modern-Art-Museum-by-Atelier-Monolit
https://visualizingarchitecture.com/texas-prairie-color-grading/
You have a good start, please keep us updated and good luck with the contest.
