Complex sentence: Van der Valk (2002), 28-9 Hermans started writing the book in 1962, during a period where he wrote exclusively first-person narratives, mostly in the present tense.
Split into simpler sentences: Van der Valk (2002), 28-9 Hermans started writing the book in 1962. In this period he wrote exclusively first-person narratives, usually in the present tense.