Consider the expression,
The book was so engaging that I could not put it down, and read it one sitting.
I am looking for a phrase, just opposite of this.
The book was so boring that it took me various installment to finish it.
I am looking for a word/phrase which has the opposite meaning to "one sitting", in the context of book reading among other thing.
Installment is a placeholder here, what word could be used to convey the same meaning.