TimeStory has an absolute maximum date range of 500,000 BC through 99,999 AD. Most timelines, of course, only need a tiny sliver of that range, often just for current, near-past, and near-future dates, but TimeStory does support building timelines of ancient history and prehistory.
To support such a large range, TimeStory divides the timeline into day-granularity and year-granularity ranges.
From 4,713 BC through 9,999 AD, you can choose any calendar day; outside that range, you can only choose individual years. (In practice, of course, we don’t have exact calendar days for most ancient dates even within that day-granularity range; this range is just a technical limit.)
You can type arbitrary dates or years into any input field using your local date conventions, such as “1/1/2025” or “50,000 BCE”. The standard Mac date-picking control does not go as far back as TimeStory supports, but within the date range, you can also click the calendar icon to pick a date.
Historical calendar details
Dates from October 4, 1582 down to TimeStory’s lower limits use the proleptic Julian calendar, and dates starting on October 15, 1582 use the Gregorian calendar. (Due to the deliberate correction applied with the new calendar, the Gregorian date October 15, 1582 immediately followed the Julian date October 4, 1582.)
Prior TimeStory version limits
Versions of TimeStory up through 3.7 (and through version 1.3 of TimeStory iPad Edition) had an absolute lower date limit of 4,713 BC, due to some internal date representation limitations. If you create a timeline with such ancient dates, it can’t be opened by these older versions.