We fly in on New Year's Day most years, and it is lighter load than usual for the airport.
That said, they also don't seem to have as many immigration stations open as they do for busier days and IF your plane lands right after one or two others, you could have a wait.
I believe the longest we've had to wait on New Year's was about 30-40 minutes, but usually it's just a few minutes and breeze right through.