Don't get fooled by skincare products that claim to "help your skin renew / detox / rejuvenate itself at night".
Our skin doesn't sleep, even though skin cells do "prioritize" different activities for the day and night time.
This is still a new area of research, but scientists have found out that epidermal stem cells differentiate (aka “decide who they want to be when they grow up”) at a higher rate at night. Also, skin cells have their highest natural UV defense on during the day (it’s still not sufficient, so use sunscreen!).
This knowledge is there, but we don’t yet know enough to be able to design products or even drugs that are aligned with the skin clock.
So for now, it makes sense to stick to basic logical reasons for differentiating your day and night time routine - things like sun protection, product consistency, immediate optical effect, photo-sensitizing effect while on the skin, and how much time you have.
And you can be sure that the brands that are currently advertising skincare products “optimized” for your “biological clocks” are BS’ing you.