Astrosecond

An astrosecond is a Cybertronian unit of time. Its precise span is unknown, but it is much, much smaller than a regular Earth second.

Writings by Dreamwave attested that (in their universe, at least) one astrosecond is equal to 0.498 Earth seconds (noting that 1000 astroseconds equals 8.3 Earth minutes, or one breem), but in the continuity that originated and made the most use of the term, the US Generation 1 TV series, astroseconds are suggested to be even shorter than that, as indicated by one instance in which seventy-two billion of them were referenced, which would equal roughly 1137 Earth years by that scale.

From Teletraan I: The Transformers Wiki, a Wikia wiki.