I am not sure where else to post this, as my question is specifically meant to be non airline specific. Moderators, please feel free to move if there is a more appropriate forum.

I have a trip to Hawaii coming up in September (Oahu). I am not sure how many Islands I am going to want to go to. I am aware that most airlines have 5K flights between islands, my question is: Will I have any luck booking these flights at 5K miles when I get there, or do I have to do that well in advance?

I have miles in all the major cariers programs, I just don't want to burn 10K if I can most likely get away with 5k.

What have your experiences been?