"deadline when" is correct and usable in written English.
For example: "Please let me know the deadline when this assignment is due."
They hit every deadline when they said they would.
Typically, the ransom increases over time until a deadline when the files are supposedly destroyed.
"The month before the big deadline when you have to show your work, I didn't sleep.
Walsh introduced more chaos at the Feb. 18 trading deadline, when he acquired six players in three deals.
Many applications have real-time constraints, which means the sink has to be informed before a deadline when an event occurs.
We journalists had been waiting for it, close to deadline, when suddenly it disappeared from the schedules.
During the five o'clock deadline, when the police threatened to go in shooting, his voice was unrecognisable.
That is the deadline when gun owners must be in compliance with the county's Handgun Record-Keeping Accountability Act.
Politicians are racing against a year-end deadline when Mr Bush's tax cuts and other stimulus measures expire and automatic spending cuts are triggered.
Washington has been fretting for months over the so-called "fiscal cliff," the Jan . 1deadline when taxes automatically rise and government spending drastically falls.
Just over a fortnight is left before the self-assessment deadline when all online tax returns must be filed along with any money owed.
