The phrase "a second deadline when" is correct and usable in written English.
It can be used when referring to an additional deadline that is contingent upon a specific event or condition.
Example: "We will set a second deadline when we receive the final approval from the board."
Alternatives: "an additional deadline when" or "a subsequent deadline when".
A broader deal is possible before a second deadline at the end of the month, when a budget deal is necessary to avoid a government shutdown.
Fehr said that George Steinbrenner, the Yankees' principal owner, first suggested extending the deadline a second time when he met with Cone on Saturday in Orlando, Fla. Fehr and General Manager Brian Cashman decided yesterday to take advantage of another seven days.
I had an awfully tight deadline when Kelly won her second gold medal at the Olympic Games in Athens, but I never panicked about the thought of my computer stopping, my telephone line not connecting or my keyboard being stuck.
The latest spate of violence began in late May, when the Qaeda group killed a Briton, Edwin Dyer, a day after its second deadline for meeting its demands expired.
The official report to the Federal Elections Commission is not due until July 15, and it is not unheard of to find disparities between what the candidates claim in the first days after the fund-raising deadline, when many are trying to drum up favorable news accounts of strong fund-raising efforts, and what they actually attest to in their filing with the government.
The second deadline was the end of this month, when Boehner planned to step down from Congress after too many fights with a band of conservatives in his party.
The victory is Halladay's third since before the July 31 nonwaiver trading deadline, when frequent rumors circulated that he would be moved to a contending team.
If the message delay is higher that its deadline, when it arrives to the receiver its contents are (temporally) invalid, which is equivalent to a deadline miss.
