NZST vs GMT — cities and working rhythm
New Zealand winter offset (April to September), UTC+12 — one of the earliest zones to open the world business day. NZ summer flips to NZDT (UTC+13). 3-4 h ahead of Sydney seasonally.
UK / Ireland / Iceland / Portugal / West Africa. Business hours 9 AM – 5:30 PM GMT typically. Note: London is on GMT in winter, BST (GMT+1) in summer — but "GMT" gets used loosely all year in scheduling contexts. Financial-services London anchors the European trading day.
Time gap: GMT is 12.0 hours behind NZST (standard-time offsets — daylight-saving flips shift this by an hour twice a year in most northern-hemisphere zones).