I've been to Oahu and spent 8 nts there and found it was just a bit too long.
What would anybody suggest for visiting Maui and the Big Island,is 5 days on each Island enough time to see everything ?.

Spent almost 1 week on Maui in February. I think it depends on who is going with you. IF it is just 2 of you, it should be enough. We were there for a week and did not get to see Haleakala. WE were with a 2 year old and the long drive to the crater just did not appeal to us after doing the road to Hana. Plan on the road to Hana to take up a full day. We did more relaxing by the beach, pool ,etc.

What are the things that you want to see, what do you want to do on each island and how busy do you want to be? That will dictate how much time you think you may need.

I can't imagine 5 days being enough to see everything on either Maui or the Big Island.

You probably don't want to take my advice though as I am someone who can spend two weeks on Kaua'i and crave another two. I don't understand 8 days being too much of any of the Hawaiian islands.

Have a great trip.

You can easily spend 8 nts on the Big Island

We spent a week on Maui and 5 days on the Big Island - it was about the right amount of time for us. On the BI, you'll probably want to stay in a couple different places to make driving easier; we stayed in Hilo for a night, in Volcano at the Kilauea Lodge for a night, and then spent 3 days on the Kohala coast at the Hapuna Beach Prince.

If you're the type that likes to drive around, stop (but not too long) at various sites, take a few pictures and head off to the next site, a week on Maui or the BI is more than enough.

If you like to "participate" say do ocean sports, hike, play golf, etc., one week is not near enough time.

Agree with travelinandgolfin.

If 5 days would have been plenty for you on Oahu, I'm guessing the same would be true for Big Island or Maui.