I visited the skydeck earlier this month, and the weather deteriorated as i got there.
The views were fantastic, and I even manged to enjoy them with a beer purchased from the refreshments facility up there.
I didn't bother trying the glass bottomed edge for an additional fee, as i have done that elsewhere several times, and with the failing weather, decided it was not worth the money.
I ended up spending over an hour there to get my monies worth and also watch the approaching storm, that failed to materialise.
In my view, an hour is probably about long enough walking around looking at the same views.