The CO agent are incorrect - the published MCT is no less than 55 minutes.
There is a 15 minute transit between the terminals for a start; then the time to get though Security and emigration.
Methinks the CO agent is thinking of USA departures.
I'd do the "Pleasantly call again" trick.
Results from ExpertFlyer.com
Code:
Minimum Connection times AKL: NZ-NZ, DOM-INT
STANDARD.D/D...D/I...I/D...I/I.
ONLINE .20 1.15 1.30 .55
OFFLINE .20 1.15 1.30 .55
** OR * ARE ALL
NZ-NZ DI 1.10 FLT 638 - FLT 739 OPN -29OCT11
NZ-NZ DI .55 FLT 302 - FLT 2
NZ-NZ DI .55 FLT 302 - FLT 31
NZ-NZ DI .55 FLT 302 - FLT 39
NZ-NZ DI .55 FLT 302 - FLT 81
NZ-NZ DI .55 FLT 302 - FLT 85
NZ-NZ DI .55 FLT 302 - FLT 97
NZ-NZ DI .55 FLT 302 - FLT 264
NZ-NZ DI .55 FLT 302 - FLT 266
NZ-NZ DI .55 FLT 302 - FLT 287
NZ-NZ DI .55 FLT 302 - FLT 289
NZ-NZ DI .55 FLT 302 - FLT 1097
NZ-NZ DI 1.00 FLT 402 - FLT 99
NZ-NZ DI 1.00 FLT 500 - FLT 221
NZ-NZ DI 1.00 FLT 500 - FLT 791
NZ-NZ DI 1.10 FLT 2226 - FLT 2
NZ-NZ DI 1.00 FLT 2750 - FLT 103
NZ-NZ DI 1.00 FLT 2750 - FLT 703
NZ-NZ DI 1.00 FLT 5070 - FLT 103
NZ-NZ DI 1.00 FLT 5070 - FLT 703
NZ-NZ DI 1.00 FLT 8408 - FLT 103
NZ-NZ DI 1.00 FLT 8408 - FLT 703
NZ-NZ DI SUP ALL - FLT 303
NZ-NZ DI 2.00 ALL - FLT 7900 - 7998