Teachers’ unions in England had complained that the timescale would not give schools enough time to prepare.
“It will take time for teachers to understand the detail,” said schools minister Nick Gibb in a letter to the National Association of Head Teachers.
Labour said the changes were causing “chaos” in schools.
Since the mid 1990s, the tests, often known as sats, have been taken by primary pupils in England to assess their ability in English and maths.
Until the latest change, this year’s deadline for schools to submit assessments by teachers of their pupils’ writing tests, would have been four weeks earlier than last year.
Schools were worried the shorter timescale would raise pressure on both staff and pupils as it coincided with higher standards demanded in the tests.