A plot twist is not a surprise — it is a revelation that recontextualizes everything the reader already knows. The best twists make the reader want to re-read from the beginning. Time your major revelations at the 75% mark of your story — late enough that the reader is invested, early enough that you have time to explore the consequences.
Minor twists can happen at chapter endings to drive the next chapter's read. To maximize your Pillar of Time (reading hours), end every third chapter on an unresolved question — not a cliffhanger, but an open door. The difference: a cliffhanger is external danger.
An open door is a question about character. 'Will she survive the battle?' is a cliffhanger. 'Will she forgive him?' is an open door — and it keeps readers reading longer..