Every in-game event window on one page, soonest first. Anything open right now sits at the top.
Holidays, Timewalking weeks, bonus events, the racing cups, Darkmoon Faire and the weekly reset come from the game's own data, so a window listed here is the window you will see in game, and the ones months out are already exact. A few rotations are published nowhere at all: those are read live, so this page can name the covenant assault that is up rather than guess at a pattern, and anything still out of reach says what it does instead of showing a date it cannot know.
The same clock runs through your achievement plan. Put in a character and any achievement locked to a window that is open right now gets a "live now" chip, floats to the top of the ranked list, and collects on its own Happening now tab, so the things you can only do this week are the first thing you see. The rest of the plan ranks every uncompleted achievement by how long it takes, quick wins first, season deadlines flagged.