Just in case you haven't heard this advice before:
If you can get the pool work and book work done before you leave, and then get a referral to a dive operator in Hawaii for your open water dives, you'll have a lot more time for "fun diving" on your vacation! At least do the book work at home, because it's a lot of reading. Maybe you could do the online coursework. Who really wants to do classes and homework on vacation?
So true! I did all of my coursework via the eLearning at home, but I actually enjoyed doing the pool work at Jack's. My instructor, Sarah Pulitzer, was fantastic and I felt it really made a difference for me that she was with me both in the pool and on the dives. For some reason the continuity made me feel very safe and confident. Not sure about Jack's but some operators give a bit of a discount on the certification program if you register for eLearning via their website registration.