how long do you need to hold a particular stock in order to get its dividend ?

Answer 1

You need to be the owner of record on the day the company declares the dividend. For most companies it is the same set of dates each year. So, check the company's web site and see what dates where used last year.

Be aware the IRS requires that you hold the stock for a certain number of days (60?) around the dividend date or the dividends are taxed as unqualified rather than qualified.

Answer 2

Dividends can be paid at any time and frequency as long as they are “legal”, meaning paid from company profits after corporation tax together with the correct preparation of documents.

Large companies tend to pay dividends once every quarter, but there is nothing in statute or tax law preventing a company from paying monthly dividends.

Answer 3

One second, as long as that second is at the end of the trading hours on the last day before the ex-dividend date. Companies pay to "owners of record at the close of business on (some date)". Companies publish announcements of their next dividend, including the date that you have to own it on. Look for "News Headlines" on finance.yahoo.com. Note that owning the stock on the day that the dividend is announced by the company, or "declared" get you nothing.
Special tax treatment requires that you own it for 61 continuous fays during the 121 day period centered on the last day before the ex-dividend date.