This is now mentioned on the Eurostar site: https://www.eurostar.com/uk-en/train/netherlands
Same info as already in the press, nothing new.
How many trains will run a day?
Two trains will depart from London St Pancras International bound for the Netherlands every day, one at 08:31 and another at 17:31.
Although travellers will need to change trains at Brussels on the way back,
How long will the journey take?
It’ll take just 3hrs 41mins to go from St Pancras International to Amsterdam Centraal.
It’s even quicker to Rotterdam – just 3hrs 1 min to be exact.