Always now
The past is always lost and the future is constantly out of reach, everything unfolds in the now.
Even when I reminisce about the past or fantasize about the future, the mood that appears is not the mood from the past event, no matter how powerful the event, but the mood which the memory evokes in the present.
In that way, past and future and even time itself can be said to be human constructs only and not really exist.
That's why letting go of the past means making room for the present and the eternal unconcernedness that fills every moment. That's also why most religions emphasise forgiveness and contentment. When the present has more room, it's easier to spot.