Firstly a double dissolution isn't currently an option, as no legislation has been twice rejected with three months in between as required by the constitution as a trigger. Indeed, and oddly, Chris Pyne decided to reintroduce his university reforms rather than set them up as a trigger.
We then get to the timing of an election. A House of Reps election can be called at any time. One must be called within ten days of the term of the house expiring, which it does three years after it first met after the last election. The house met on 12 November 2013, so election needs to be called by 22 November. If it was called that late we'd be voting on Christmas Day.
But to keep the house elections aligned the timing of Senate elections comes into play. A Senate election cannot be held more than twelve months before the term of the Senators expires, which is 30 June 2017! So a combined Senate and HoR election is only possible in the window between 1 July 2016 and the requisite period (I think 42 days) after 22 November. My money in on some time in October or November 2016.
Of course, were the PM crazy brave and decide to go for an HoR only NOW he could wait much closer to 30 June 2017 and have simultaneous elections. That would have been a great strategy now if he was facing Senate obstruction AND was leading in the polls. It wouldn't unblock the senate but would set up a great 2017 strategy.
Who knows ... Maybe he will convince himself that an election would focus the electorates mind.