Help regarding selling property

Any how you will have to pay the capital gain tax.

you can sell the flat whenever you want. Take help of a local lawyer/broker. Your tax, etc, will depend on many factor such as your income, the value of the property (e.g. if the property is valued at more than Rs.50 Lakhs, you may have to cut TDS and deposit with the government immediately), etc.

You need to provide details.