it should be 6 months
Do you have any link for this information? What I have read your residence permit is valid up to 30 days after you loose the job. You have an obligation to notify your regional office about the change of employment within 15 days - the governor's will probably issue a decision on revoking your temporary permit's validity. In its decision the province governor will determine a deadline for you to leave Poland.
You are also probably aware that you can't change this job (either employer or a workplace) if your stay in Poland on the basis of the blue card permit is shorter than 2 years?