Why Some Countries Use 30-Minute Time Zone Offsets
Most time zones are neat hourly offsets from UTC. UTC+1, UTC+5, UTC-8. Clean. Simple. But some countries looked at that system and said, "Nah, let's use half-hours."
Why? The answer is usually geography and politics.
India: UTC+5:30
India spans nearly 30 degrees of longitude — enough for two time zones. But India chose one: UTC+5:30, a compromise between the eastern and western parts of the country. Kolkata (in the east) sees sunrise around 4:30 AM in summer, while Gujarat (in the west) sees it around 6:30 AM. Both are on the same clock time.
The half-hour offset puts India roughly halfway between Pakistan (UTC+5) and Bangladesh (UTC+6). It's a political middle ground as much as a geographic one.
Iran: UTC+3:30
Iran's offset puts it 30 minutes ahead of its western neighbors (Iraq, Saudi Arabia on UTC+3) and 30 minutes behind Afghanistan (UTC+4:30) to the east. Iran also has DST (UTC+4:30 in summer), which means in summer it shares Afghanistan's offset. In winter, it's unique.
Nepal: UTC+5:45
The strangest offset in the world. Nepal is 45 minutes ahead of India, its massive neighbor. The reason: Nepal wanted to assert independence from India's time zone. The 45-minute offset puts Nepal roughly aligned with its geographic position (about 86°E longitude, which is 5h44m from UTC). It's one of only two 45-minute offsets in the world.
The Other 45: Chatham Islands (UTC+12:45)
New Zealand's Chatham Islands use UTC+12:45 in winter, UTC+13:45 in summer. They're 45 minutes ahead of mainland New Zealand. The reason is geographic: the Chathams are significantly east of the New Zealand mainland, and a full +13 offset would put them too far ahead of their solar time.
Australia's Patchwork
Australia has three standard offsets in its mainland: UTC+8 (Western), UTC+9:30 (Central), UTC+10 (Eastern). The half-hour offset in the center means that driving from Perth to Sydney, you change your watch twice — not once. And Lord Howe Island uses UTC+10:30 in winter, UTC+11 in summer (a 30-minute DST shift, which is unique).
Why Not Just Round?
You could argue that India should just be UTC+6 (like Bangladesh). But then sunrise in Mumbai would be at 7:30 AM in winter — late by Indian standards. The half-hour offset is a compromise that keeps sunrise and dinner at "reasonable" clock times across the country.
Half-hour offsets are annoying for software developers. They're great for the people who live there.