8 feeds sounds normal in a 24 hour period. As for lenghth of time I'm not totally sure. My bubs was feeding about 20 mins but she didn't put on as much weight as the MCHN would have liked so she has told me to try and get her to take at least another 5 mins on other side.
But every baby is different and yours may not need as much time as he may be more effective at draining out the milk. If he is putting on weight and having wet nappied I wouldn't be too concerned. If it does worry you maybe call your MCHN and ask her opinion. Does your baby seem full after a feed or is he wanting more 30 mins or so after you have finished?