I just spent a week in Aalsmeer, which is a 40 minute bike ride from Amsterdam (or a 40 minute drive). Since it doesn’t have a train station it was inconvenient to get anywhere without a car. That said, if you are near a train station, pretty much all the major cities are within 30ish minutes of one another.
That said, I think it’s more a function of the Netherlands being a small, flat and dense country than having great public transit. You could probably bike between most major cities in less than 90 minutes.
Interesting view of the Netherlands, but you can't reach most of the ten largest cities in the Netherlands within 30 minutes by train or 90 by bicycle from most of the other cities. Eindhoven, Groningen, Tilburg, Breda, Nijmegen are all quite a distance from Amsterdam, and even the rail journey from Almere to Rotterdam takes over an hour.
That said, I think it’s more a function of the Netherlands being a small, flat and dense country than having great public transit. You could probably bike between most major cities in less than 90 minutes.