Time arbitrage is mostly at the millisecond time scale, not microsecond.  For instance there is massive investment in microwave data transmission between New York and Chicago.  Microwaves in air go close to speed of light in vacuum, while the more typical fiberoptic data links are at the speed of light in glass, about 30-some percent slower.  The microwave links beat the fiberoptic by about 2 milliseconds on New York to Chicago, which is enough to arbitrage between markets located in those places.