Acid enhanced ionic liquid (IL) 1-n-butyl-3-methylimidazolium chloride ([C(4)mim]Cl) pretreatment has shown great potential for boosting the yield of sugars from biomass cost-effectively and environmental-friendly. Pretreatment with shorter processing time will promote the commercial viability. In this work, pretreatment of reduced Amberlyst catalysis time of 34 min was demonstrated to be the most effective among time-varying pretreatments, evidenced by partial removal of hemicellulose and cellulose crystal transformation of Arundo donax Linn. A higher fermentable sugar concentration of 10.42 g/L (2% substrate) was obtained after 72 h of saccharification than the others. Total processing time to reach 92% glucose yield was cut down to approximately 26 h. Progressive deconstruction of crop cell wall was occurred with increased catalysis time by gradual releasing of H3O+ of Amberlyst. However, vast lignin re-deposited polymers on fibers could hinder further enzymatic hydrolysis. These discoveries provide new insights into a more economic pretreatment for bioethanol production. (C) 2015 Elsevier Ltd. All rights reserved.