how to account for FYA in NPV calculation

Strictly it depends on when the asset is bought. If it is bought on the last day of an accounting period, then the allowance is calculated immediately and so the tax effect will be either immediate (if no delay) or at time 1 (if one year delay).
If, however, the asset is bought on the first day of an accounting period, then the tax effect is calculated at the end of the accounting period (i.e. 1 year later) and so the tax effect is at time 1 (if no delay) or at time 2 (if one year delay).
However the examiner does not usually give the date and is then flexible about what assumption you make.

thanks.

Why would you depreciate the asset for the whole year in the moment of buying it? Shouldn´t the depreciation start from the moment we start to use the asset? I would think that for instance if we buy asset at the end of year 1 and from that moment start to use it, the first annual depreciation will be accounted at the end of year 2.
Please could you let us know your opinion?

Thank you.

This is not accounting depreciation - it is capital allowances (tax allowable depreciation). You first get capital allowances (in full) in the accounting year in which you make the purchase.

Thanks John, I ´m aware that we are talking here about tax allowable depreciation, but it all depends on the country in question. I assume you´re talking about UK tax rules, in other countries obviously other tax rules would apply, so important to read well the question and as you mentioned, if not clear from question better to make assumption.

I am talking about UK tax rules, but unfortunately the examiner does not usually state that rule - he gives the capital allowance rate and usually says whether tax is payable immediately or with a one year delay. However usually that is all.
His answers follow UK tax rules, but for the reasons you give the marking is usually fairly flexible with regard to the tax.