The Japanese campaign to conquer the Netherlands East Indies began on December 7, 1941. They had reached their major objectives by March 8, 1942 when the Dutch Army in Java surrendered.
However, KNIL units on Sumatra and Australians and KNIL troops on Timor carried on the fight for a while. The KNIL troops on Sumatra capitulated late March 1942. A few hundred Australians and Dutch started a deadly guerrilla campaign on Timor in March 1942. It tied up an entire Japanese division of over 12.000 men and lasted well into 1943!
I have posted a chronology of the total campaign under ‘Military Background’