Eye drops are usually used at anytime when you want. Whenever you feel eye dry, you can use eye drops. Even if you wearing contact lenses, you can use some eye drops to help you keep moist. Nevertheless, there still some people believed that using too much eye drops will do harm to eyes since eye drops contain preservatives. And the believe tears is the best water to keep eye moist.
In my opinion, you'd better use lubricating eye drops when needed. When your eyes get dry, you can apply lubricating eye drops to keep your eyes moist. People who often work at the computer screen for a long time are easy to get dry eyes. In this case, they can take a bottle of lubricating eye drops with them. Once they feel dry in the eyes, they can put several drops of the lubricating eye drops to keep the eyes moist.