The Genshin Impact PS5 version will be ready to go as soon as PS5 arrives, thanks to an incoming update.
Developer MiHoYo revealed its plans for Genshin Impact version 1.1 today; the largest update to the free-to-play game yet is coming on November 11 and will add new quests, characters, and a seasonal event called "Unreconciled Stars." It will also add PS5 compatibility to the game, which is perfectly timed since the console will start hitting shelves the day after that.
According to MiHoYo, Genshin Impact will be able to run on PS5 "via backwards compatibility with improved graphics and faster load times." Genshin Impact is already a beautiful-looking game on PS4, both in its sprawling world and its colorful character designs, so getting a graphical boost there sounds like a treat.
That initial load screen when you're logging back into the game can be pretty hefty as well, so improvements would be welcome. I doubt Genshin Impact will ever be totally load-screen-free on PS5, since it will still need to do the usual connecting-to-servers stuff as an online service-based game, but hopefully there will be less waiting when you log in.
Since all of your progress is linked to your MiHoYo account, it should be relatively painless to switch from playing on PS4 to PS5. You should still make sure you have your account details handy when you go to make the switch, just in case.
The developers of Genshin Impact have been keeping players in the loop with a Q&A for frequent feedback.