[coherentpony]

The circumference of Earth at the equator is about 40,000 km and the speed of light is about 300,000 km/s. The appropriate division results in about 0.13 s.

That seems to track. The vast majority of requests won’t go half way around the Earth, so maybe halving that time at 0.06 seems like a reasonable target.

[AnonC]

Light travels at about 0.69c in fiber optic cables (c being the speed of light in vacuum, which, as you stated, is about 300,000 km/s).

[coherentpony]

Ah yes I forgot about that. Thanks for the correction.