4. Remember how long you have been putting this off, how many times you have been given a period of grace by the gods and not used it. It is high time now for you to understand the universe of which you are a part, and the governor of that universe of whom you constitute an emanation: and that there is a limit circumscribed to your time - if you do not use it to clear away your clouds, it will be gone, and you will be gone, and the opportunity will not return.
5. Every hour of the day give vigorous attention, as a Roman and as a man, to the performance of the task in hand with precise analysis, with unaffected dignity, with human sympathy, with dispassionate justice - and to vacating your mind from all its other thoughts. And you will achieve this vacation if you perform each action as if it were the last of your life: freed, that is, from all lack of aim, from all passion-led deviation from the ordinance of reason, from pretence, from love of self, from dissatisfaction with what fate has dealt you. You see how few things a man needs to master for the settled flow of a godfearing life. The gods themselves ask nothing more of one who keeps these observances.
6. Self-harm, my soul, you are doing self-harm: and you will have no more opportunity for self-respect. Life for each of us is a mere moment, and this life of yours is nearly over, while you still show yourself no honour, but let your own welfare depend on other people's souls.
Procrastination - that thief of time and will. Sometimes, I have procrastinated a certain task and I am glad I did, due to the fact that the task was no longer required or due to the fact the scope or requirement changed. And my procrastination saved me time. However, in the context of what Marcus is saying in Book 2, verses 4-6, he is talking about grander, more important things. He is referring to life; and learning the lessons of life and not wasting it away. He is talking about amor fati and being willing to accept the universal forces in action. Furthermore, he is trying to convey the seriousness of the present - the NOW.
We do not have control over the past nor the future. The only thing we have control over is the present. And if we waste away the present watching TV, flipping through social media, eating food and lazing around, as opposed to being mindful, helping others, acting logically, then we will have not only wasted the present, but all future present moments.
The purpose of thinking that we may die at any moment and that we should "perform each action as if it were the last" of our life, is to help us appreciate the vast importance of NOW.
To finish, let me quote Hadot on this point (p. 135 The Inner Citadel):
The thought of death confers seriousness, infinite value, and splendor to every present instant of life. "To perform each of life's actions as if it were the last" means to live the present instant with such intensity and such love that, in a sense, an entire lifetime is contained and completed within it.
Most people are not alive, because they do not live in the present, but are always outside of themselves, alienated, and dragged backwards and forwards by the past and by the present. They do not know that the present is the only point at which they are truly themselves and free. The present is the only point which, thanks to our action and our consciousness, gives us access to the totality of the world.