Morning or night, when to use a serum
People ask this expecting a rule. The honest answer is that the timing matters less than the consistency, with one practical exception.
The case for night
Nothing is going on top of it, you are not about to put on makeup, and you are not about to go out in the sun. It also attaches to an existing habit, which is why it tends to stick.
The case for morning
Skin that is holding water looks better through the day. If you would rather see it in daylight, use it in the morning and give it a minute before anything goes over the top.
The exception
If you are also using something your doctor or pharmacist gave you, follow their instruction on timing over anything a product page tells you.