Less Than Two Hours
According to the Canadian Partnership For Consumer Food Safety Education, perishable dairy products such as dips that have cream cheese or sour cream in them should not remain at room temperature beyond two hours.
Dips On Ice May Keep Longer
The University of Nebraska at Lincoln Extension says that salads and other chilled foods such as dips "can be left out as long as they are kept on ice." Placing dip in a serving tray with an ice compartment underneath can keep dips safe for longer.
Dairy based dips, including cream cheese dips, must be properly cooled in order to remain in a room temperature environent beyond two hours. The University of Nebraska at Lincoln recommends that if you do not have a serving tray with an ice compartment, try putting out small bowls of dip intermittently as they are used rather than letting one large bowl sit. Replace serving utensils when you replace the dip and avoid adding fresh dip to dip that has sat out beyond two hours.