how do I know when to consider an estate "closed"

what is the standard in determining when an estate is considered "closed". This is a small family estate with 1 beneficiary. The last check was written from the estate bank account in early May of this year leaving that account now at zero. I plan to go close the estate bank account this week since it is no longer in use.

 

Is the estate considered closed based on the day you close the estate account or is it a date I can choose?

Also I believe we have 4 months to file the 1041 from the date the estate closes, correct?

 

Thanks