Most task apps have one date field doing two jobs, which is why their users have forty "overdue" items and no idea which ones matter. Real Momentum keeps the two meanings apart on purpose.
A when-date answers "when do I intend to do this?" It's what puts a task in Today when the day arrives, and what lays out Upcoming. It is a plan, and plans move — rescheduling a when-date is planning, not failure. A task with no when-date isn't unloved; it just lives in Anytime until you pick its day.
A deadline answers "when is this actually due?" — a date with an external consequence attached. The filing closes, the fare goes up, the client walks. Deadlines show a countdown as they approach and turn red when missed, and they mean it. That signal only works if you don't pollute it: if missing the date costs nothing, it's not a deadline — it's a when-date.
The two compose naturally: deadline Friday, when-date Wednesday. The deadline is the cliff; the when-date is where you plan to stop walking toward it. Most tasks, honestly, need neither.
A when-date says which day; a time block says which hour, and defends it. From any task you can create a time block — a real event on your real calendar, which shows up in Calendar.app, on your phone, and as busy time to anyone trying to book you. Move or resize the event and the app follows; done either place is done both places.
With calendar access granted, Today and Upcoming interleave your events with your tasks, so the day you're planning is the day that actually exists — the one with four hours of meetings in it, not the imaginary ten-hour one.
When-date → surfaces the task in Today on that day; you'll move
it freely, and that's fine.
Deadline → countdown as it nears, red when missed; reserved for
real consequences.
Time block → an hour on your actual calendar, synced both ways,
visible everywhere your calendar is.