I cannot imagine that this would be enough time. If the land is actually open to the general public that day - and sometimes “special” preview days are not. I was at BG on “press day” for their new coaster last year, and no one but press was allowed to ride (even though there was virtually no line all day).
So if it is announced that Pandora will be open to the public as well, I would guess that people will be lining up an hour or two before park opening and will head straight toward Pandora. I’m guessing most will head to FOP first, but there will definitely be an “instant crowd” at both. If you’re near the head of the line, you will probably be able to get the first one done in 45 min (or maybe less), but I can’t imagine you’ll have less than a 60 minute wait for the second. The “pundits” are predicting “triple digit” SB lines for both attractions for most of the day - at least for the first few months. The “general wisdom” for after Pandora officially opens is to get an FPP for one of the rides and hit the other right at RD (along with hundreds of others).
Another possibility is that the special previews will be in the AM and they will open it to the general public after noon. If that’s the case SB lines will be long at both attractions - as well as the line just to get into Pandora.
Of course, ALL of this is pure conjecture based on past “big openings”. Who knows - outside of Disney “inner circle” fans (e.g. the people who don’t know what an ADR is or how to book FPPs or want to know where Harry Potter is), peopel may not even know about Pandora and there may not be a huge clamoring to get in (let’s face it, Pandora does not have the following of HP nor the name recognition of Snow White).
All a long way of saying that if the multitude of stars and planets were all in perfect alignment you possibly could do both in 45 min (with no lines, the queue/ride time for each is probably in the 10-15 minute range, and the two rides are right next to each other) - but I would find that HIGHLY unlikely…