When does life insurance check from your mother passing away how long does it take to come in?

This does not happen automatically. You need to visit the insurance company and take care of some formalities.

Case 1: Your mother has made you her nominee for the policy. In this case you need to show proof to the insurance company that your mother has passed away, and you are her son and also give them the insurance policy number/document.

Case 2: If your mother has not made any nominee for her policy, you need to provide all the proofs mentioned in case 1 + proof that you are legal hier.

Once you complete the formalities, the company would issue the check in a few days depending on their service agreement details mentioned in the policy (This differs from company to company & country to country) Usually it should not take you more than 2 weeks.