Vanguard's site said there was a premium, but at what time was there a premium? At about the time that the US market closed?
If so, then it is a bit complicated.
If there is a premium at a time when foreign markets are open, and you can capture that premium, fine. But if those foreign markets are closed and US markets are open, and the world changes, and US stocks trade and change prices, that premium might be an illusion.
This is complicated by some foreign markets being open at times, and some being closed. Some foreign stocks trade in the US, some don't. Some trade in US as ADRs. Some foreign stocks trade on other foreign exchanges. Some trade on other foreign exchanges as GDRs.
A sophisticated investor can make estimates of value using this data, and estimate the value of stocks that are not currently trading such as by comparing other similar stocks from other countries that are trading. They can then decide if the premium is really a discount, or if the premium is really a larger premium, etc. When the US market is open they can trade the ETF, using underlying shares and the trading basket, making profit. In theory, this should keep the premium/discount low. But only low enough to pay their costs plus a profit. It is expensive to trade underlying foreign shares. Vanguard can probably step in too to keep the discount/premium from being too high; I'm not aware of methods, but since they have the dual structure, there may be ways, and they might even benefit the funds. They also have motivation to protect customers, though I suspect that ETF traders may be low on that list.
If there is demand for an ETF, there might be a small premium. If people are selling it, there might be a small discount. I don't mean the premium or discount you see, I mean after accounting for the true fair market value of the underlying shares, which will really be a matter of opinion when foreign markets are closed. This is because the manner of accounting for the shares which are not trading anywhere can be handled in different ways by different analysts.