Complex sentence: Olson has left and rejoined Trouble three times; he was in the band from 1979 to 1986, and again from 1993 to 1996, when the band was on hiatus.
Split into simpler sentences: Olson has left and rejoined Trouble three times. He was in the band from 1979 to 1986 and 1993 to 1996, when the band went on hiatus.