Gratuity provisions in a private limited company

Dear Members,

I am seeking an advise on keeping a provision of payable gratuity as an expense. The questions are as follows:

1. Can an organization book the payable gratuity as an expense in balance sheet
2. What will be the tax implication on it for an organisation 
3. How the profit will be calculated for a particular financial year – will that be including this liability  (Gratuity) or excluding it.
4. Can we book this liability from the first year of the employee or it can be only after completion of 5 year

Looking forward to your answers.

Best