Sentence:  The time interval of an <WSD>occurrence</WSD>—a temporal instantiation—is a single occasion. However, a series of such occasions can fall within a certain time interval; in this case we may represent the <WSD>occurrence</WSD> as a single situation (cf. "I ran off and on for an hour, I ran and ran for an hour, I would run and then run some more"). 
Meaning of the word marked with <WSD> tags:  The lexical aspect (aktionsart) of verbs or predicates that change in or over time.