This is not a change of strategy says Downing Street.
This is not a new timetable, they say.
However, the prime minister's declaration that he wants British troops home by the next election does highlight the fact that his mind is on how and when to bring British forces out of Afghanistan.
David Cameron has repeatedly said that he does not view Britain's military commitment as open-ended.
In November last year he talked about imposing a "tight internal timetable". In April, he said that Britain would put everything into the fight "this year and next year" and said that "we've been there already for eight or nine years. That's already a long time. We can't be there for another eight or nine years".
He went on: "It's got to be in the next parliament that these troops really start coming home - as soon as possible but based on success, not on an artificial timetable."
On all those occasions, though, David Cameron was not prime minister. That's why his comments on Sky News that "we can't be there for another five years" are significant.
Earlier today he discussed Afghanistan with the host of this year's G8, Canada's Prime Minister Stephen Harper. In March 2008, Canada's parliament voted to pull the troops out of the war in 2011 (although members of its Commons Special Committee on the Canadian Mission in Afghanistan have spoken of maintaining a role after that date).
Tomorrow he will lead the G8's discussion of Afghanistan and hold a bilateral meeting with President Obama, who has committed to troop withdrawals from next year.
On his mind, and theirs, is the fact that June has been the bloodiest month for Nato forces in Afghanistan since the mission began in 2001, with the coalition death toll standing at 80.
What's more, he and they know that we are entering fighting season and that, as the prime minister said onboard the Ark Royal yesterday, we need to brace ourselves for a "difficult summer".
The prime minister's message to the military is that this is the year the generals get to show they can make progress.
What today's remarks suggest is that he may be thinking already about what to do if they don't make that progress.
PS: In another interview - with Canadian broadcasters CBC - the prime minister spells out his thinking on Afghanistan in more detail :
Q: The three major partners in this, the United States, Great Britain and Canada - the US and Canada both set dates already. The US saying they're going to start to withdraw in July of next year, Canada saying they're out as of the end of next year. Are you looking at a date?
A: I haven't named a date in that way, but obviously all of us, as I've said many times, we don't want to be in Afghanistan for a day longer than we have to be. As soon as the Afghans can take control of their own security then we shall be bringing our troops back home.
We shall go on having a very long and deep relationship with both Afghanistan and Pakistan. We've got to convince those countries that we're in for the long haul with aid, with diplomacy, with trade, with assistance. We don't want those countries to go back to being the bad lands for terrorist training camps, but do I want to get the troops out? Yes, of course I do.
Q: Why do you hesitate on a date when others seem to be rushing towards one?
A: Look, I accept the timeframes that have been set out by President Obama and I'm working very closely with him. A proper review of how we're doing towards the end of this year, the ambition that we should be starting to transition districts and then provinces of Afghanistan over to lead Afghan control by the end of this year and into next year and then, yes, the ambition to start bringing some troops home.
But I want this to be done, as far as possible, on the basis of success rather than lines in the sand and dates, but am I pushing very hard to get everything done so this can happen? Yes, of course, and I think there are basically three elements: it's making sure the surge works and the counter-insurgency is going full steam ahead. It's about training up the Afghan army and police, and then, vitally, it's about the political settlement that we need to make with those elements of the Taliban that want to lay down their weapons.
Get those three things right and the timetables are realistic.