Conflict between two sections sec 152(3) & sec 156

practically you can apply for DIN at any time...they just need ID cards and basic stuff...but then there should be company now and so you have to communicate DIN to prove that you have proceeded further and used your DIN in specific company...

Basically, section 156 use the word EXISTING DIRECTOR means existing director at the time of commencement of the act are required to intimate the companies wherein HE IS DIRECTOR at the time of commencement of the act.
Section 152 is completely different section which imposes an obligation on person who is going to appoint as director in any company to acquire the DIN and intimate the company about his DIN

( After the CA Amendment,2017 central government may specify any other no. in place if DIN no.)