Unix time and why leap seconds are weird
Unix time counts seconds since 1970-01-01 00:00:00 UTC, ignoring leap seconds. 1757328000 is just 'that many seconds after the epoch' — timezones only enter when humans want to read it.
It matters because it is the lingua franca of logs, APIs and databases: one integer, no timezone ambiguity, sortable by nature. Whenever systems disagree about 'what time is it', compare epoch values.
Mistakes: mixing seconds with milliseconds (×1000 bugs), assuming local time is UTC, and forgetting 32-bit signed overflow on 2038-01-19 (use 64-bit). Leap seconds make 'every day has 86400 s' slightly false.
Example: 2026-09-08T00:00:00Z = 1788297600. In ms that is 1788297600000 — APIs that expect seconds will read it as year 58647.
Try: Unix Timestamp Converter · 2038 & Limits Checker
Business-days math across holidays
Business-day math counts Monday–Friday and skips your holiday list. The trap is that 'holidays' are per-country, per-region, sometimes per-company — no formula knows your calendar.
It matters for SLAs, delivery promises, invoicing terms ('net 10 business days') and project plans. Off-by-one errors here become missed deadlines and contract disputes.
Mistakes: counting the start day, forgetting Easter-shifted holidays, ignoring half-days, and assuming weekends are Sat–Sun everywhere (much of the Middle East rests Fri–Sat).
Example: Sep 1 → Sep 30, 2026 with no holidays = 22 business days. Add Sep 8 as a holiday → 21. Always pass your exact holiday list.
Try: Business Days Calculator · Days Between Dates
Pomodoro that sticks: intervals that work
Pomodoro is 25 minutes of single-task focus, 5 of real break, and every fourth break 15–30 minutes. The timer is a commitment device, not a productivity score.
It works because starting is harder than continuing: a short, honest interval lowers the activation energy, and the break protects attention from degrading into fake work.
Mistakes: skipping breaks ('I'll rest when done' — you won't), counting interrupted pomodoros as complete, and choosing tasks too big for one interval. Split first, then time.
Example: a 3-hour essay = six 25/5 cycles with a 20-minute break after the fourth. Log sessions locally and watch completed focus time, not hours sat down.
Try: Pomodoro Timer · Study Timer
DST transitions without surprises
Daylight-saving transitions delete or duplicate an hour: in spring the clock jumps 02:00→03:00 (that hour never exists); in autumn 02:00 happens twice. Meetings inside those windows shift or vanish.
It matters because rules differ by hemisphere and change by law — the converter shows the explicit offset per zone so you see the jump instead of guessing.
Mistakes: assuming every zone springs forward the same weekend, storing local times without offsets, and recurring meetings that drift after a transition.
Example: a weekly 02:30 call US to EU disappears on the US spring-forward Sunday. Move it to 03:30 that week.
Try: Time Zone Converter · Meeting Planner
Deadlines you can take anywhere
A deadline is a timestamp plus a timezone: Friday 5pm means nothing across zones, but epoch 1788297600 is the same instant everywhere. Track the instant, display it local.
It matters for distributed teams: the tracker counts down to one epoch value while each member sees their own wall-clock equivalent.
Mistakes: EOD Friday without a zone, daylight shifts moving the local reading mid-countdown, and comparing formatted strings instead of epoch integers.
Example: deadline 2026-09-08T00:00:00Z = epoch 1788297600 — Madrid reads 02:00, New York 20:00 the day before. Same instant, no argument.
Try: Deadline Tracker · Unix Timestamp Converter