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According to instructions for the form 706 - http://www.irs.gov/pub/irs-pdf/i706.pdf - see page 30 - here are estimated average times.
However - the form 706 would be needed only for estates above $3,500,000 (for decedents died in 2009).
You would also need to file final tax return for the decedent and estate income tax return - form 1041.
You may need to become familiar with the IRS publication 559 - http://www.irs.gov/pub/irs-pdf/p559.pdf
Generally - expenses to manage the estate is between 3-5% of the estate value.
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