Can I work when I receive my receipt for my i-485 and i-765 when its based on IR (Immediate Relative) of a USC?

A receipt is not evidence of authorization to work in the United States. It will not meet the requirements of the I-9 Employment Eligibility Form that you will be required to complete when you apply for work. So, an employer would not be able to hire you as meeting the I-9 requirements with only the receipt notice. You will have to wait until you receive the  actual work permit document.