I drove by there today and the gate was closed on the Hill County side. Not even boat access from the looks of it.
I've watched the water come up several mornings and it does come up faster, but it's not like a sudden surge or a tidal wave. There's plenty of time to get out. However, by the time it gets here it's had 9 miles to stretch out and that may not be indicative of what happens at the dam.
The article I read implied but didn't state that in the previous system they would sound the horn and let the water out gradually. The new system sounds like they blow the horn and let it rip all at once. More of an instant full flow, and about 500 cfs more now than before to boot.
I'd need to be there and see it happen to really understand how fast and high it will come up now. Not much odds of me being there though.