I use the Alternate Start - Live Another Life mod just so I don't have to put up with the urgency created by the dialogue of the game. There are no time limits on anything but they way they word things, it always feels like there is. I also use Immediate Dragons so I can still kill the beasties. As long as I refrain from speaking to Jarl Balgruuf, the main quest-line will not trigger; I can enter and leave Whiterun at my leisure, go where I want, do what I want to do and there is no one nagging me about the Greybeards. Sure the guards will mumble something about dragonborn IF they actually see me kill a dragon but those are just old wives tales, right?