$1$ year $=365$ days; standard relationships apply between seconds, minutes, hours, days, weeks, and months — always check which unit the question wants before converting.

15:15 means 3.15 p.m.; 03:15 means 3.15 a.m. When adding a duration to a 24-hour time and the total reaches or passes 24:00, subtract $24$ hours and move the date forward by one day.

Time zones are given relative to UTC/GMT — e.g. UTC$+8$ means $8$ hours ahead of UTC. To convert a local time from one zone to another, add or subtract the difference between their offsets, remembering that moving to a zone with a larger offset means adding time.

Worked Example

A flight leaves London (UTC$+0$) at 23:40 on Monday. The flight takes $11$ hours $50$ minutes. The destination, Singapore, is UTC$+8$. Find the local day and time of arrival in Singapore.

1. Add the flight duration in London time: $23{:}40 + 11\text{h }50\text{min} = 35{:}30$.
2. This exceeds $24$ hours, so subtract $24{:}00$ and move the day forward by one: $35{:}30 - 24{:}00 = 11{:}30$ on Tuesday (London time).
3. Convert to Singapore local time by adding the $8$-hour zone difference: $11{:}30 + 8{:}00 = 19{:}30$.
4. This stays within the same day, so arrival is 19:30 on Tuesday, Singapore time.

These conversions chain together for less direct questions — e.g. converting a duration given in seconds into hours means dividing by $60$ twice, then by $24$ if it also needs to become days.

Subtract the start time from the end time by working in whole minutes throughout, borrowing an hour (as $60$ minutes) if the minutes of the start time are larger than the minutes of the end time — exactly like column subtraction, but base $60$ instead of base $10$.

Worked Example

A train departs at 09:45 and arrives at 13:20. Find the journey time.

1. Minutes: $20 - 45$ can't be done directly, so borrow $1$ hour ($60$ minutes) from the hours column: $80 - 45 = 35$ minutes.
2. Hours: since $1$ hour was borrowed, compute $13 - 1 - 9 = 3$ hours.
3. The journey takes $3$ hours $35$ minutes.