It is very tempting to use skin care products one after the other in quick succession, but to maximize the effectiveness of the products, you should give your serums and medicated creams or ointments time to really absorb into the skin before applying your moisturizer.
Why is this important?
Giving the product a minute or two to absorb (a) helps it to dry fully, preventing piling under make-up or sticky feeling; (b) allows the product (esp. topical prescriptions) to treat the target area by lessening the chance of it getting spread to other areas.
How much time should you allow?
At least one minute, even for “fast-drying” serums, is recommended, but I have known dermatologists and aestheticians who recommend up to 5 minutes. Unless the directions or your dermatologist state otherwise, one or two minutes should be sufficient time for most products to absorb while also reducing the risk of dryness or oiliness that can happen if people accidently wait too long to moisturize.
To save time while also giving the serum or cream time to absorb, try doing other short healthcare steps in between applications. For example, apply your nightly serum and then brush your teeth before applying your moisturizer. That makes the most of that 1-2 minute “absorption break.” I would recommend, however, that you avoid doing your hair during the break in order to reduce the risk of accidently transferring hair oils onto your skin.