I think you are pretty fine if you manage to jump on NEX @ Tokyo station around 6:30 (or similar time at Ueon for the Keisei Skyliner), you should arrive airport around 7:30 which should give enough time for check-in / security. That means you need to wake up at 5 and check-out at 5:45 or so, depend your hotel in Tokyo
If that sound too crazy for you, goto Narita one night before makes lots of sense (and you can take the cheap Keisei commuter train as well)