I used DNS assay for detecting the presence of reducing sugars after a 10 min reaction (purified xylanolytic enzyme with 3% xylan) and it worked for me. 

Basically 200 uL of your substrate at a given pH, add 50 uL of your enzyme solution and let it react for the time stipulated (you'll have to play with the enzyme concentration and reaction time). After the reaction time add 500 uL of DNS. put them at 100ºC for 10min and the ice them for another 10. Read ABS at 546nm.

Then you'll have to transform the ABS into IU/mg of protein.

See the file for details.