Some measurements with a logic analyzer and the Raspberry Pi 2
sleep: 0.001500, measured avg: 0.0015357, measured 0.95 perc.: 0.0015573
sleep: 0.0185, measured avg: 0.0186177, measured 0.95 perc.: 0.0186345
servo_pulse_oversleep was set to account for the (expected) overhead of waking up and toggling the pin with help from the numbers above.