it took about 2 hours for the install after the download. I am guessing a lot of folks downloading. I did mine soon after it was released. With me, I have a fusion drive and 32G ram. So converting the file system probably was part of that 2 hours.
I had no problems launching my apps, although some which are 32 , received a notice that the manufacture needed to upgrade to 64 bit. Eh...
With each Beta, I would assume a lot to a little change and the load time is compromised.
With Weathercat, the initial start up took a while, but subsequent startups went fast.
I do like the dark screen easier on my eyes to a point.