At the hardware level, it takes 0 time (10's of microseconds at most for I2C connected codecs, maybe a millisecond for USB 2.0 sound card) to mute the mic input

At the hardware level, it takes 0 time (10's of microseconds at most for I2C connected codecs, maybe a millisecond for USB 2.0 sound card) to mute the mic input channel to the mixer sitting before the A/D converter. If it takes any more than 0 time, it's caused by badly written software. I wouldn't blame the HW for the privacy issues, here.