Ye get the 'normal' number of gains per day that ye would without the scroll.
The time between gains remains the same.
However, the scroll increases the number of points ye can gain at a time.
The daily RoT cap is also ignored.
The only way to get the maximum gain from the scroll is to log out inbetween gains, in a safe place.
I am open to correction, but I believe the maximum gain per attempt is .5, so, if ye were able to squeeze all of thy daily 21 gains into one scroll, ye could potentially gain as much as 10.5 in a given skill.