The phrase "extension granted" is correct and usable in written English.
It is typically used to indicate that an individual or organization has been allowed a period of extra time to complete a task, fulfill a requirement, etc. Example sentence: The principal asked the student to complete the essay within a week, but upon hearing the student's explanation she granted an extension for another two days.
P2 extension granted: everything is due W Mar 31.
Conoco and Marathon have a license to export liquefied natural gas from Alaska to Asia until 2013, under an extension granted last year.
The extension granted to France and others immediately raised eyebrows among some analysts, who said these countries might use them as an excuse to relax their reform efforts.
The deadline extension, granted by the United States Olympic Committee, resulted from necessity, as the roster as of late seems to need an N.F.L.-style injury report.
Remo Rabaiotti who had been working in the takeaway for the last 10 years, put a petition on his counter to argue that the site should have the extension granted.
His most recent contract extension, granted in December 2013 after Denmark had failed to qualify for the 2014 World Cup finals in Brazil, was not greeted with wide acclaim.
Applicants will submit their completed applications no later than the deadlines stated below with no exceptions or extensions granted.
Applicants will submit their completed applications no later than March 1, 2015 with no exceptions or extensions granted.
May 9 Wednesday Termination of occupancy in Teachers College residence halls for spring term for students not remaining for summer session A. Extensions granted for students participating in Commencement.
May 10 Wednesday Termination of occupancy in Teachers College residence halls for Spring Term for students not remaining for Summer Session A. Extensions granted for students participating in Commencement.
May 13 Wednesday Termination of occupancy in Teachers College residence halls for spring term for students not remaining for summer session A. Extensions granted for students participating in Commencement.
