Defered tax

Is it mandatory to consider preliminary expenses as timing difference while calculating deferred tax liablity of a company in subsequent years of commencement of business (Please go through the following instance)..? For Eg: Preliminay Expenses incurred by a company is Rs.25,000 which is written off over a period of 5 years as a matter of prudence for normal accounting purposes. whereas preliminary expenses allowable u/s 35D of the Income tax act 1961 is coming around Rs. 5,000 which will be amortized in 5 equal installments over a period of 5 years. So Rs.20,000 (25000-5000)  is a permanent difference as only Rs. 5,000 is allowable u/s 35D of the IT Act. whether Rs.5,000 is considered as timing difference or Rs.25,000 is considered as timing difference for the purpose of deferred tax calculation. How much amount of preliminary expenses would be considered for deferred tax calculation in first year and in subsequent years..?