If you are serious about the study and ready to dedicate 6 to 7 hours daily, you may prepare the syllabus within 4 months. There are many students who got success within 4 months of preparation.
Elementary and Advanced Mathematics by Kiran Publication is the best book for SSC CHSL Mathematics preparation.
Quantitative Aptitude for Competitive Examinations by RS Agrawal is the best book for SSC CHSL Quantitative Aptitude preparation.
General Knowledge 2022 by Manohar Pandey is the best book for SSC CHSL General Awareness preparation.