Thanks for posting your questions - we're Aussie based & also planning an Alaskan cruise with HAL, but for 2024 and have been tossing up between a b2b, or the 14 day explorer; this has been really helpful!
We were on Ovation a couple of weeks ago; our boarding time was 2pm - we had lunch nearby, and by 1pm the line to check in was much shorter & they opened it up to all remaining time slots, so like us you may be on board earlier than you expect.