In order to be eligible for payment, how soon do you need to be entered in a dividend stock to receive the div?

You're eligible for a dividend if you own the stock before the ex-date. If you missed that date initially, then you will be eligible for the dividend in the next quarter.

It depends how you have your brokerage account set up. Dividends can be reinvested which means the dividend will be used to buy more shares. Otherwise, the dividend will go to your core cash account that your brokerage account uses.

You have to own the stock on the record date to receive the dividend. The record date will be a part of the dividend announcement by the company, which the company will typically release as a press release as well as file with the SEC. Your broker should also note the record date as well. Call your broker to find out how to access that information as access to it varies by broker. The "ex-date" is investor jargon for the day after the record date. There is no hold requirement for the stock to receive the dividend. You could own the stock only for only one day, as long as it is the record date, and receive the full dividend.

If you do not have a dividend reinvestment plan (DIP) set up, then the dividend amount will go to the cash balance in your brokerage account. If you do have dividend reinvestment, then it will be used to purchase additional shares of that stock. Check with your broker to see if a DIP is available and if you are automatically enrolled.