Commentary on Meditations: B6:32

I am made of body and soul. Now to the poor body all things are indifferent, as it cannot even make any distinction. To the mind all that is not its own activity is indifferent: and its own activities are all in its control. But within these the mind is only concerned with the present: its activities in the future and in the past are also indifferent at any present moment.

Marcus marks a clear delineation between things which are up to him and things which are not. Things which are not up to him, are indifferents and he (his mind) can have any opinion about them that he wants. As to time, the only thing relevant to him is the present. There is nothing that can be done to change the past and the future is truly not up to us. A million different things could alter any plans we may make. The only thing up to us is our present attitude and volition. 

(see also Citadel p. 113, 131-132)