From the article:
6,500km cable length
148 (& 149) amplifiers
66.5 (& 66.9) ms of round trip latency
Wikipedia says the refractive index of typical optical fibres is 1.44
So the light travel time down 6500km of fibre would be 6,500x10^3/(3^10^8*1.44) = 0.0312ms, and twice that for the round trip = 62.4ms
From that we get that the total latency of 66.5ms is 62.4ms of light travel time plus 4.1ms of (presumably) inline amplifier and terminating equipment latency.
That means each of the 148 amplifiers are doing their thing in something less than 28 microseconds, possibly way less since it'd be easy to assume the terminating equipment at each end is doing a way more time consuming task that just amplifying the signal, so could easily be taking up the bulk of that 4.1ms non-travel-time latency.
Anyone know how those amps work?