The demand, and the clock
When an assessment raises a tax demand, it is formalised in a notice of demand under Section 156, and that notice is what makes the amount payable, within 30 days of service. If you do not pay within the 30 days, interest starts running under Section 220(2) at 1% for every month or part of a month it stays unpaid, and you are treated as in default, which opens the door to recovery.
For an NRI that recovery is not abstract. The department can attach your Indian property and issue a garnishee notice to your Indian bank, requiring the bank to pay your balances over towards the demand, and it can pursue an agent or representative of yours in India. So a disputed demand left unaddressed is a genuine risk to your Indian assets. But you do not have to choose between paying it in full and doing nothing.
Staying the demand while you appeal
If you appeal the assessment, you can apply to the officer under Section 220(6) to treat you as not in default in respect of the disputed demand, which stays recovery while the appeal is pending. The officer has discretion here, and the well-known benchmark is that a stay is generally granted on your paying 20% of the disputed demand, holding the rest until the appeal is decided.
The important thing to understand is that the 20% is administrative practice set by internal instructions, not a figure written into the law, so it is not a rigid pre-condition. The officer is meant to apply an independent mind to your case, and can grant a stay on paying less where the facts justify it, for instance where the demand looks likely to be deleted on appeal. So it is worth asking for a stay on terms suited to your case, not simply assuming you must pay 20%. A practising CA files the appeal, applies for the stay under Section 220(6) on the best terms available, and heads off recovery against your Indian accounts and property while the dispute runs.