Dropping a rock on your toe is simple mechanics.
Getting it to un-drop after the fact is a chore of a higher magnitude. Maybe reality only has 'room' for a tiney set of actualized events and for an event to get accepted into the fold, as real, it has to be witnessed by an existing member of the group. Maybe EVERYTHING has happened but we do not consider it so untill we SEE it happen.
Time then, would be an interconnected biological energy field produced, in concert, by a group of living beings who agreed on what is happening in their 'right now'. Time could also be macaroni & cheeze....given enough believers.