You've been able to watch enough of the video to discern that the moderator was an equal-opportunity-interruptor? Honest question, I just skimmed the video, and given that there were 5 men of similar age/race, I don't think even if I were in the audience I'd have a clear tally on how much each man got to speak, versus how easy it is to track how much/little opportunity the woman had. But the OP does assert that the moderator even acknowledged to Dr. Hubeny that she hadn't had much time,. Looking at the time period around 1 hour in, it does seem that he talks excessively while questioning Hubeny. But I didn't sit and watch all of the other interactions he had with the men.
Just because the moderator had interrupted some of the other speakers does not mean the OP is wrong in her assessment that Hubeny was egregiously talked-over. I guess if you think the sexism claim is unwarranted, you could help skeptics by linking to timestamps where Holt gives other panelists the same intensity of talk-over he allegedly gave Hubeny.
Edit: I'll play a little Devil's advocate to help the discussion.
At 39:25, the moderator is going on length about...something. His cadence wavers as if inviting anyone to jump in, but he keeps on going: https://youtu.be/Er7qPv8jsZo?t=39m26s
30 seconds later, he finally asks why inflation has such skepticism and points to a panelist. The panelist tells a kind of rambling joke and as he rambles through the punchline, the moderator steps in and moves on to the next question:
https://youtu.be/Er7qPv8jsZo?t=39m50s
Arguably, though, you could say the moderator did the right thing because the panelist made a kind of weak joke, and the moderator had to interject to go onto the next topic. He ends up explaining, in a way that I imagine is more accessible to the audience, the 2 fields of thought, before pointing to another panelist:
https://www.youtube.com/watch?v=Er7qPv8jsZo&feature=youtu.be...
This panelist is given a decent chunk of time to talk, almost 2 minutes, to go over string theory, etc.
At 1:02:00, he pitches to Dr. Hubeny, and he gives her the same treatment in which he takes a good long time to set up the question and the scope that's understandable to the audience, while being a useful topic for her:
https://youtu.be/Er7qPv8jsZo?t=1h1m55s
At about 30 seconds in, as he's describing her position (presumably to the audience), she tries to clarify something , but he keeps talking. However, i think this is case of her misreading the moderator's pause as a cue. About 10 seconds later he finishes his train of thought and cedes the floor to her at around 1:03:00: https://www.youtube.com/watch?v=Er7qPv8jsZo&feature=youtu.be...
But about 20 seconds later, as she's trying to assert how both theories are correct, the moderator jumps in say "So tell us about those 2 theories".
https://youtu.be/Er7qPv8jsZo?t=1h3m21s
...which is fine, because maybe he sensed the speaker was going to go too deep into details about the equivalence of the 2 models, when the audience would benefit from her describing the models.
...However, this interruption goes on for almost a minute, as he apparently decides to do the work of describing the theories. He eventually stops talking and reverts back to his prior prompt of "tell us a little bit about the 2 theories"
https://www.youtube.com/watch?v=Er7qPv8jsZo&feature=youtu.be...
Hubeny appears ready to speak, but the moderator then goes on for 10 more seconds in which he tries to explain to her what he wants her to explain...and this is where Hubeny "giggles". But she's given about a full minute to talk, which seems reasonable.
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I don't present the above points as complete evidence, it's what I landed on after randomly scrubbing in the period before the 60 minute mark. I think it's not out-of-line to say that the moderator is aggressive/over-eager in talking too much, and it may not just be sexism. But when you have a panel of 5 men and 1 woman and the woman has had little to speak for 60 minutes in, that's a bad time to go on an extended interruption as he did, as it becomes very noticable.
That said, I don't want to say that the moderator is a total ass. He has 6 highly intelligent and possibly highly specialized people who don't have a unifying topic of debate, so it's incumbent upon him to not only define a scope that the audience can relate to, but aggressively move the discussion forward so that no one rambles too far into their rabbit hole.