Im not sure you can get the very exact time input was received, just because the nature of computers, there is always going to be a time gap between when input is received and the computer can respond. I think setting a variable as soon as input is received is about as close as you can get, so close in fact I do not think the time gap could even be humanly preceivable. And if that is not acurate enough, im courious to know why you would need greater accuracy.