My guess is that it would be possible, but you probably won't have a very good viewing spot for the fireworks. Previously PtN was about 17 minutes in length; so I would allow a few extra minutes now for the added float (so let's say 20 minutes). You'll need to watch from near the start of the route, get through DCA to the entrance, get through the DL ticket gates and then find a spot. In theory, yes, you could do it, but it might be cutting it close.
As dina44444 said, it might be better to try and watch fireworks first and then see the second PtN (if that is an option). My feeling is that the PtN route is fairly long, so unless you're going opening weekend, you stand a better chance of finding a decent spot along the route for the second showing of PtN than you would finding a good fireworks viewing spot close to show time.