The first seasonal markets usually begin in November, with the greatest choice from late November through December. Some winter events continue into the first week of January.
Most Dutch markets run for a single day or a single weekend rather than for weeks. The season concentrates mostly on two weekends, 11th to 13th December and 19th to 20th December, with 44 markets open on Saturday 12th December alone. The long-running exceptions are the Valkenburg cave markets, 13th November to 30th December, and Magisch Maastricht, 27th November to 27th December.
Generally, yes. Major Christmas markets in Belgian cities often run for several weeks, making them easier to include in a December visit. Smaller local markets may still only take place on selected dates.