Again, I don't think I've particularly waited any great deal of time for any vista. It's not hard to keep track of when and where to be for a vista to be available.
I've waited for hours on top of the wood post in North Shroud (great "vista" btw, very realistic and breathtaking) because I wasn't sure when I would be able to successfully jump on top of it again, and that's how long it took for the proper time/weather condition to show up again. It took me nearly a couple hours to get on top of it the first time, which is also how I missed its window the first time.

At least when I finally managed to scale the Kugane tower, that was it; I could get my vista and it was done, no waiting around. (Just don't get me started on the lamppost vista they only added in later to be total jerks...)