taxman415 and I are correct. There are no limits to the amount of elite night credits you can earn. Here is a copy of the terms about this benefit from the Chase website:
You will earn 1 Elite night credit for each $3,000 in net purchases. There is no limit to the number of Elite nights that you can earn. Please allow 6-8 weeks for Elite nights to be credited to your Marriott Rewards account from the last day of each calendar month you qualify. Purchases do not include balance transfers, any checks that are used to access your account, cash advances, cash-like charges such as travelers checks, foreign currency, money orders, overdraft advances, interest charges, unauthorized or fraudulent charges, or fees of any kind including fees for products that protect or insure the balance of your account. We have the right to determine which purchases qualify for this offer. We reserve the right to change or end this offer at any time. To qualify for the Elite nights, your account must be open and not in default at the time of processing and fulfillment. Chase is not responsible for offer fulfillment or the provision of or failure to provide the stated benefits and services.