Book entry date for goods imported...

Hi Friends,

Can someone help me about........

Purchase Entry for goods imported has to be done on......1) Invoice Date or; 2) the date of Custom Clearance or  on the date of goods received into the factory.?

Also, Exchange rate of the date on which we book the entry for purchase of goods is applicable.

For E.g.: Inv. Dt.: 05-June,  Bill of Entry Dt.: 15-July, and  CHA Rcpt. Dt.: 20-July. (Goods Received in factory)

On which date purchase entry is to book & Exchange rate of which date is to use?

Thanks in advance,

Ajay