From the wikipedia article:

"The definition of a mora varies. In 1968, American linguist James D. McCawley defined it as "something of which a long syllable consists of two and a short syllable consists of one".

It's unclear to me in my readings, whether moras have to do with applying categorical perception to durations, or whether more strongly they imply that each "count" is literally the same duration of time.

For an example of the weaker statement, it could be that the first mora takes 1 unit of time, and the second mora takes somewhere between 1/2 and 1 units of time. The additional time, so long as it's not too short or long, pushes the perception of the duration into the second category.

The stronger statement says that each mora takes the same unit of time to articulate.