According to the H&R Block web site the Federal Gov. has no inheritance tax.

it was hard to collect the tax, so the state followed the feds by repealing the inheritance tax laws and inacting an estate tax. basically the tax was paid by the estate before it was distributed to the heirs

There is no time frame. If you are a resident of the state when you inherit, you pay the inheritance tax per the state laws.

Washington DC does have an estate tax. They do not have an inheritance tax. It would be a good idea to consult a probate attorney in DC. They will know how to reduce the tax liabilities of the estate.

Burt Rufus Glidden has written:

'Inheritance and estate tax laws (annotated)' -- subject(s): Inheritance and transfer tax