Wellington is typically 2 hours ahead of Sydney. Both observe DST but switch on different dates, causing the difference to vary between 1-3 hours at transitions. Generally Wellington is 2 hours ahead.
New Zealand uses NZST/NZDT while Australia's east coast uses AEST/AEDT.
Business hours overlap well! 9:00 AM - 5:00 PM Sydney corresponds to approximately 11:00 AM - 7:00 PM Wellington. Trans-Tasman business coordination is easy.
Wellington and Sydney are connected by frequent 3-hour flights. Air New Zealand and Qantas operate multiple daily services.