Time zones
Why do some time zones have 30- or 45-minute offsets?
Half-hour and quarter-hour offsets are reminders that civil time is chosen for people, not forced into a 24-box diagram.
Offsets do not have to be whole hours
UTC offsets describe a local civil clock relative to UTC. They are often an integer number of hours, but there is no physical requirement for that. India uses UTC+5:30, Nepal uses UTC+5:45 and Newfoundland uses UTC−3:30.
They can better fit geography or policy
A half-hour can place a shared civil clock nearer a region’s solar rhythm than the nearest whole-hour choice. It can also distinguish a country’s clock from its neighbours while keeping a nationally useful standard.
Never round an offset in software
A fixed “UTC plus five” assumption loses real information. Good scheduling software stores an IANA zone and asks for the offset on the relevant date, including any daylight-saving transition, rather than inferring it from a nearby capital.