Job with business

since it is a private company, please refer to your company policy/rules book

GO thru the T&C/service conditions in appointment letter, and other policy/rules mentioned in appointment that shall govern the service conditions say HR policy/Service Rules and regulations, standing orders applicable to establsihment and you......................

Assuming that if these do not prohibit as on date then also you shall be at the disposal of employer during the applicable work/OT hours.