OP - Do not wait 10 seconds more. Your legal rights to a chargeback expired at 60 days and you say that you have been trying for over 2 months. Most major card issuers (banks) permit substantially longer (often up to a year).

It should take you <5 minutes to initiate the dispute online. You should make clear that the property has promised the refund but has not processed it. This will put the shoe on the other foot, e.g. for Marriott / property to explain why the credit should not be offered. Given that it has been promised, it is unlikely that the property does anything and you will have a permanent credit.

For the benefit of others, if an initial call / email does not promptly resolve an issue such as this, initiate the dispute immediately. No reason to let any deadlines pass and no reason for you to be out the case / credit.