Mueller will probably finish his report, with or without Trump's testimony, long before the Nov. elections, and of course, that will not be the end of it. I'm just wondering about the preferred timing for this thing to roll out by all affected. Mueller has to be thinking about the coming election and how and in what particular climate his report is going to be received. Even without any political bias motivations, there is still much to be considered with regards to expediency, especially if he is going to recommend specific courses of action.
One would assume he'll try to appear as neutral and apolitical as possible, given how things went down in the last election. That may be impossible given Trump's instinct to pick a fight when cornered, like most common criminals, but also given the everyone's unquenchable appetite for leaks.