If you rely on the fact of separation, you will need to be separated for a period of 3 years (if your spouse consents to the divorce), or 4 years (if there is no consent to the divorce).

If you rely on desertion, you will need to show that your spouse has deserted you for a continuous period of 2 years before filing for divorce. 

However, if you are filing for divorce under adultery, unreasonable behavior or mutual agreement, there is no period of separation required before you can file for divorce.