How long can I store par cooked French fries at room temperature?A:
In the olden days, proprietors of restaurants or fast food joints would cut the potatoes and par cook or blanch in the morning for use the whole day, returning the unused fry strips to the walk-in or refrigeration in the evening. More recently, the issue has been reviewed by public health departments and they typically recommend no more than ninety minutes at room temperatures or the time of the serving period (such as thru lunch or dinner). Are you frying different products in the oil? Food safety issues can be possible contaminated seasoning or breading in the oil, workers handling the fries with open cuts on their hands or food matter falling onto the uncovered room temperature potatoes. The pathogens that can multiply do not go away with finish frying.
So, it’s best to cut, blanch, let cool and then refrigerate whenever possible.
Good French fry tips here: How to Make the Best "Signature" Fresh French Fries