What is the ruling on answering some questions in a job application exam by chance or speculation due to time constraints and their difficulty?

An exam is designed to assess the level of the examinee. If the examinee answers based on knowledge, or a strong presumption, or even by taking a chance—due to the difficulty of the questions or limited time—then the answer was obtained without cheating. There is no blame on him for this, and he will be treated according to his results.