This one's interesting. Betfair call it their Wining Wednesdays.
Every Wednesday at a random time they take a snapshot of all players currently logged into the Casino.
£1000 prize money is then divided equally and given to all those players.
You get the cash the next day.
The terms say:
So log-in first thing in the morning, place a $5 bet and stay logged in for the rest of the day!Eligible customers are customers who have engaged in real money play in the Betfair Casino and who are logged in at the time that Betfair Casino chooses to select the winners