Experience Amsterdam
Offers an explanation of the country's complicated business hours, as well as lots of other essential facts.
http://www.experienceamsterdam.com/amsterdam_basics.html

Holland.com
Details Dutch opening times.
http://www2.holland.com/global/index.html?page=http://www2.
holland.com/global/geninfo/practinfo/bushour.html

Trade Port
Includes details of opening hours in Holland, among other things.
http://www.tradeport.org/countries/netherlands/01grw.html