Of course the deadline is October.
But Pierre Axe The Tax Poilievre was determined to force one as soon as possible, still is. He (his party) was riding high in the polls for almost two years but have dropped a lot in the last couple of months.
Either we have an election now or we re-open Parliament. In Parliament there would be a No Confidence motion. If the NDP vote with the Liberals they would keep the government in power. They have dropped in the polls as the Conservatives have fallen and the Liberals risen as Carney looked like winning and then won the leadership. If there is an election now the NDP will be squeezed so they might have.
Carney has done a quick calculation based on the idea that now with the wind in his sails is the best time to seek a mandate. Many Canadians want a strong capable leader right now while under this economic back stab by our one-time friend. Right now, Mr Axe The Tax is view as perhaps a bit too much adjacent to tRump and tRumpism / Muckism.
Though Doug Ford is Conservative, he just won a majority in Ontario's election by running as a "strong leader", anti-tRump despite previous embraces. Carney is sensing that being a credible counter to tRump-Lutnick-Bessant is a winning play right now.