Asti, it is; kāya, a body: five of the six substances have extension, occupy many space-points at once, and are called astikāyas. Time does not and is not.
Souls, matter, the two media and space each spread over space-points - innumerable, or infinite, or in matter anything from one upward - and their points form a whole, a kāya. Time, in the traditions that count it a substance at all, has no such spread: its units do not join into a body, and even the Digambara kālāṇu sits one to a point and never combines. So the Pañcāstikāya, Kundakunda's text of that name, is about five things, and the sixth is treated apart.
The atlas draws the five on the first view as things with area, and time as ticks along the foot, which is the drawn form of the same distinction.
The six, compared as the sūtra compares them - The five astikāyas highlighted