When it comes to chapter length, there are no hard and fast rules. What matters most is that the chapters fit the story, not the other way around. Many novelists today prefer chapters that range from 1,500 words (or six book pages) to 8,000 words (or 32 book pages).
However, this does not mean that chapters longer than 8,000 words are necessarily too long. Depending on the story, 20 pages may be the perfect length for a chapter. It all depends on the flow of the story and the pace at which the author wants to move the plot forward.
For example, if the chapter is a key turning point in the story, then a longer chapter may be necessary to fully develop the characters and the plot. On the other hand, if the chapter is more of a transitional chapter, then a shorter chapter may be more appropriate.
Ultimately, the length of a chapter should be determined by the story itself. The author should consider the plot, the characters, and the pacing of the story when deciding how long a chapter should be. If a chapter is 20 pages long and it fits the story, then it is not too long.
In conclusion, there are no rules when it comes to chapter length. The important thing is to make sure that the chapters fit the story, not the other way around. Depending on the story, 20 pages may be the perfect length for a chapter.