Why is there a pause before the light comes on/mac starts charging when plugging in?
This is only educated speculation, but I imagine it's related to the amount of switching that has to take place when changing from battery power to being on the mains. The electrical input needs to be registered, the hardware switched from running off battery to a charging state if needed, and time for the kernel to be informed of the state change based on the polling frequency. Then the other power management daemons have to pick up the state change and the OS get the message that the power state has changed. If that polling was taking place at intervals of less than a few seconds, I'd be surprised.