The account only has to be open for 120 days. It doesn't even have to have a balance in it. It just has to be open.
You just give Member Accounting the DVA number. That's how it worked last year. I don't know how it will work this year. According to the FAQs for the DVA, you are not supposed to be able to pay your
DVC dues with the account. Your payment may or may not qualify for the $20 bonus for each $1K spent.
Another thing to keep in mind is that your maintenance fees will be due before you reach the 120-day mark if you have not already opened a DVA. Your DVC account needs to be paid by Jan. 15 and will be considered past due on Feb. 15 regardless of your UY.