。
I spent hours reading books.
Literal
Books [object-を] read-[sequential-て] what-hours-[emphatic-も] passed.
何時間も ('many hours,' literally 'what-hours-also') is a common emphatic construction: 何 + counter + も expresses 'many' or 'as many as.' 過ごす ('to spend [time]') pairs naturally with time expressions. The ~て form links the activity (reading) to the outcome (time passing). Subject (the speaker) is omitted.