Some people tell me that even if it is very simple to do, you have to hold it for some time.
To answer this, it's important to understand, who are those people. You coworkers? Friends? Family? Your boss?
If it's your boss, you should probably listen. There might be valid reasons to hold the job for some reasonable time.
How often it happened to you that after you've done something, you were told, "Oh, you are done already? The customers decided they don't need it after all", or something to that effect. Or your boss may give you that assignment in advance, for you to think it over, or to prioritize your work, but not to start until it's final that you actually need to do it.
On the other hand, if it's your coworkers tell you that, first think about their motives. (See posts above.)
If it's friends and family, they might want to teach you how to look "busy and important" - you don't have time to do such a small task right away, you have other priorities. Or to make a task small to you to look more difficult and time-consuming to the "outside" people. You can always ask them what they mean, and, of course, decide for yourself.