Good point, normally AKL is reasonably efficient but I once had it take an hour from landing until deplaning due to delay in getting a gate. So delay for another plane could affect your connection, and with separate tickets there isn't a minute to spare in the original schedule. I'd change to an earlier flight unless not caring about missing the SQ plane (also in the past SQ tends to be overbooked and looking for an excuse to offload pax, esp. on codeshares ... so don't expect any grace period on checkin time).