And think about it, Disney does not want you booking from the comfort of your living room, or the comfort of an off site hotel that they're not getting a cut of. They want you to suffer if you're not staying on site. And right, I think its completely logical to think that grown adults (and their children) are capable of getting to the park within 60 minutes of their time being called.
But this may all be moot. There are rumors that you may be able to book within ~60 minutes or so. But I've also heard rumors that you have to be on Disney property (remember, Disney property is really, really big). Until this plays out for real or Disney themselves says anything, its all speculation. I think that the most logical assumption would be that you have to be on site. Why would Disney forgo a chance to upsell on site hotel stays?