Let me just say...It is totally worth your time to side trip here. My friend and I came to the Hague with the sole purpose of seeing Vermeer's "A Girl with a Pearl Earring" and it was worth the ticket and the train ride.
When you go, try to make it early in the morning when they first open up. In a museum as small as this crowds can be a pain. Every wall of the museum is covered in well selected masterpieces, no space is wasted on filler. I can safely say this is one of the best museums in Holland. Simply because it is simple and the pieces are well selected and displayed.
They are open Tues-Sat 10:00am to 5:00pm; Sundays and holidays 11-5. They are closed Mondays.
The cost is minimal...maybe 10 euro.
From journal Art and Amsterdamming