From page 8 of the 1041 instructions:
When To File
For calendar year estates and trusts,
file Form 1041 and Schedule(s) K-1 on
or before April 15, 2008. For fiscal year
estates and trusts, file Form 1041 by
the 15th day of the 4th month following
the close of the tax year. For example,
an estate that has a tax year that ends
on April 30, 2008, must file Form 1041
by August 15, 2008. If the due date falls
on a Saturday, Sunday, or legal
holiday, file on the next business day.