Are there any rules by which the Assessing Officer has to comply regarding sending Assessment Order to an Income Tax Assessee (provided the Assessee has filed Satisfactory Return & on time) ?

Meaning , is there some Time – Frame by which he has to compulsorily send Assessment Order to Assessee after the filing of Return is over?

What does the Income Tax Act say on this Aspect ?

Is it true that after Direct Tax Code comes into effect , Assessment Officer can reopen Income Tax file of any Assessee at any time (even after Assessment Order has already been issued for that particular year ?