Due date for payment of wages

Dear! Here there are two laws that you might be dealt with. The Wages Act (for a salary less than Rs. 18,000 /- P.M) and Order 37 of CPC if the salary is more than Rs. 18,000 /- P.M. Now if the contractor is paying less than Rs. 18000/- P.M to the labour that you are concerned with here, then you will refer to the section 5 of the Wages Act regarding the law that will be applicable. So the salary is the first factor to be kept in mind.

The second factor is the number of employees, as you mentioned. If the number of employees under him are less than 1000, the Wages Act is again the right call. So yes, you can refer to the Wages Act. 
 

Payment of Wages Act is applicable to Contractors even and therefore Section 5 of the Act is applicable to them as well.

Yes you can refer section 5 of Wages Act.