You can use skincare serums at night, and during the day. In the daytime, if you've got dry skin, wash your face and pat it dry, then layer your skin with a serum that quenches the skin's thirst for nutrition, wait for a few minutes for it to settle down. Follow up with a moisturising sunscreen of your choice. If you can cleanse and rinse off this layer once in the afternoon, and reapply it, it would be ideal. For the night, try not to layer too much and instead let your skin breathe. Most night creams tend to be quite concentrated anyway, so either use them or a night serum not both. However, the key is not to overuse so don't apply it night and day.