IGG now allows you to keep your campaign open indefinitely after you hit your goal, in order to get "slacker backers," etc. without going to a separate service.
Our plan is to run the campaign for about 40 days (the sweet spot based on IGG's data) and, assuming it's successful, we'll leave the campaign open until the game launches in 2017/2018.
Right now we're thinking that physical rewards will still be available to latecomers until early 2016, and then after that it will only be digital or upgrades.
And all of these will apply to stretch goals, most likely. Or at least up to some cut-off date.
So... on one hand, if you can't support us during the campaign, all is not lost! But in order for us to get to that point, we need to succeed.