I just want to get there early enough and get to the lounge to have a nightcap after having spent the entire day travelling with a 4 yr old and a 1 yr old..... With my luck I'll check in and the lounge will have closed 5 minutes prior.
It sounds like you are staying club level. If that's the case, you should be escorted tothe lounge/ceck-in area upon arrival. If the lounge is still open, then you will be able to get something.
In that sense, it shouldn't really matter if you do online check-in.
If you are talking about the main resort lounge, then you also should be able to get a drink before checking-in, since the check-in staff would be available 24 hours. Hope that makes sense.
Beyond that, I've done CL both ways (Online and regular check-in) in the last year. I haven't found a clear cut advantage to doing online check-in if you are staying club level. Either way, you have to meet with a staff member at check-in. The information you provide online is pretty limited, and only slightly expedites the process, if at all. As far as I can tell, they basically confirm the information with you regardless, so the time difference is minimal. Perhaps I should clarify, I've only done CL at AKL once - the other CL stays were at different resorts.
The real benefit of online check-in is to bypass the main lobby chek-in line, not the check-in process itself. Even there, at most resorts, at most times of day the difference is minimal, and I say this as someone who dislikes wasting time on vacation. The "online check-in line' is generally very short, but most regular check-in lines are not very long either - especially if you are arriving late.
I wouldn't worry about it at all. I would not bother trying more than once a day, if that, over the ten available days you get. If it doesn't work, don't give it a second thought.