You are required ton pay bonus to all employees within 8 months from the end of the financial year.
There isn't any specific provisions for separated employees. So the same rule applies to them also.
Therefore you are free to give it along with all the others within 8 months. Most companies give it along with full and final because otherwise they have to find the employee and give him the money later. If you do not give it to him then it must be noted in the unpaid bonus register and after 3 years deposited in the labour welfare fund.
Another thing to be noted is that you are talking of Diwali bonus not statutory bonus. If you are paying customary bonus (like at Diwali or Dasara) then you can adjust that at th time of annual bonus. It means in effect you paid bonus during the year and not at the end of the year and therefore you done need to pay anything more now (there are circumstances you need to verify). However it's actually unfair b cause you probably didn't pay to those who are newly joined
Sharpening the focus of Mr. Saswata Banerjee, permit me only add by way of clarification the following:
1) There is no need to pay the Bonus to the separated employee along with the F & F settlement.
2) Bonus is always paid for the previous financial year.
3) You need to pay Bonus within eight months from the close of the financial year to covered employees and who have put in more than 30 days service during the concerned year.
4) If Bonus is paid to employees not covered under Payment of Bonus Act 1965, as a term of employment then you must make the payment along with F & F settlement only.
June 30, 2015
However, paying it then is the easiest way. If you don't you need to find him and pay later, which is more complicated.
If he is not under bonus act, but eligible for bonus (under settlement or terms of appointment letter) then it should be paid along with full and final. There is no justification for paying it later.
One problem is some companies don't know at time of resignation how much bonus will finally be declared. In that case you have no option but to wait till accounts are finalised and bonus amount computed.