This concept depends on how big your manufacturing concern is. If your manufacturing concern is big enough that it has 100 employees, model standing orders under THE INDUSTRIAL EMPLOYMENT (STANDING ORDERS) ACT, 1946 shall be applicable to your concern, which talks about the casual leaves of 10 days to be given to an employee other than the leaves available to him under the Factories Act Chapter VIII. The probation period is also given as 3 months for such concerns. However, the Model Standing Orders are silent on the eligibility part, meaning since when these leaves shall be accrued by the employee.
Hence, it gives scope for interpretation and policy-making on the part of the Management. If you seek my opinion, I would suggest allowing him at least 1 leave per month until the expiry of his probation period, but in case of grave sickness, he should be given the maximum possible leaves.
In the case of fewer employees, it would be at the discretion of the Management, but again, I would suggest that at least 1 leave should be provided to the employee while on probation as leaves are related to employee benefit, and all labor laws being beneficial legislations, we need to give them the most liberal interpretation possible. Please note that the concept of casual leaves is only given under the Model Standing Orders under THE INDUSTRIAL EMPLOYMENT (STANDING ORDERS) ACT, 1946 and not under the Factories Act. That is why I said that employees should be given leaves as per the discretion of the Management.
Feel free to revert in case of any doubt.
Regards