Once a car accident claim settles, the check itself usually arrives within a few weeks. After you sign the settlement release, the insurer issues payment to your attorney, who deposits it and handles the next steps before the money is disbursed to you.
A few things can add time. Any liens — bills a medical provider or health plan is entitled to be repaid from the settlement — usually have to be resolved first, and negotiating them down protects your net recovery. Extra paperwork, and court approval for a minor's settlement, can also add time.
The longer part of the process is usually reaching a settlement in the first place, not cashing the check. That is one reason it often makes sense not to rush a settlement before your injuries are understood.