In most cases, you will receive your Casino Credits within 72 hours of the end of a promotion period if you have successfully opted-in the promotion and met the terms of the promotion, including any playthrough requirements.
This Help Center article can help you check if you opted into a promotion.
Note: If you've opted into a promotion, met the requirements, and it has been over 72 hours after the end of the promotion period, please contact DraftKings Customer Support Team for further assistance.