How long can margarine be left out of the refrigerator?

Leaving a stick or “quarter” of hard margarine at room temperature for a day should be fine, but manufacturers recommend refrigerating soft tub margarine promptly after use. Stick margarine’s high amount of saturated fats and trans fats protect its texture and flavor. However, soft margarine (margarine in tubs) loses its shape, texture, and flavor if left at room temperature because it contains polyunsaturated and/or monounsaturated fats, which eventually oxidize, become liquid, and perhaps go rancid at room temperature. It’s difficult to say how long a particular soft margarine product may be left out of the fridge as it depends on various factors: degree of heat it is exposed to, the amount of emulsifiers and antioxidants that have been added to prolong shelf life, and the proportion of polyunsaturated and monounsaturated fats. (Polyunsaturated fats spoil faster.)
 
A spokesperson at Land O’ Lakes consumer help line said to return margarine to the fridge immediately after use. Unilever advises customers not to eat its I Can’t Believe It’s Not Butter! margarine if it has been left out overnight or at 70° F or higher temperature “for an extended period of time.” The margarine won’t be unsafe, but it will not have its intended high-quality flavor and consistency, especially once the tub has been opened.
 
Source(s):
Cleveland Clinic: Heart and Vascular Health & Prevention
Land O’ Lakes consumer help line: 1-800-328-4155
I Can’t Believe It’s Not Butter! consumer help line: 1-800-634-0302