In respect to extension two events are mutually related so that either (i) one includes the other, or (ii) one overlaps the other without complete inclusion, or (iii) they are entirely separate.

But great care is required in the definition of spatial and temporal elements from this basis in order to avoid tacit limitations really depending on undefined relations and properties.
Such fallacies can be avoided by taking account of two elements in our experience, namely, (i) our observational 'present,' and (ii) our 'percipient event.' Our observational 'present' is what I call a 'duration.' It is the whole of nature apprehended in our immediate observation.

It has therefore the nature of an event, but possesses a peculiar completeness which marks out such durations as a special type of events inherent in nature.

A duration is not instantaneous.

It is all that there is of nature with certain temporal limitations.