I have not personally hiked this section yet. I have been doing a lot of research on it for this summer. Section J is most commonly done in 4 days and 3 nights. I have seen trip reports from people who have completed it within 3 days. I would only recommend that if you are an experienced hiker, are comfortable hiking 25 miles each day, and are comfortable with extreme elevation loss/gain. It is definitely doable! Just make sure you are well prepared.
I have read in August there are a ton of bugs. Highly suggest a bug net for over your face!
Most importantly, have fun & be safe!