Monday thru Thursday they don't open until 8:00am, but open at 7:00am Friday thru Sunday. If you can, get there for the weekend time and be a little early. They sometimes open up a little earlier than 7:00am. It depends on when the ranger shows. The light is better early, heat not as bad but humidity is always there.
For your first time I would walk 40 Acre Lake. This is the first parking lot to your left after passing the ranger station where you pay. Walk down the north side of the lake, past the Observation Tower to the Spillway Bridge and then come back, turning left at the tower to finish that trail. The light can get harsh pretty quick, so you can shoot in the shade from the tower to the bridge, and on the east side of 40 Acre on the way back. As far as interesting things to shoot...you could go every day of the year and see something different. That depends on your skills as a photographer and how well you "see" things.
I do know there are a few Barred Owls that hang out in the area from the tower, back to the spillway and then back to the east side of 40 Acre lake running about halfway down that side. Scan left to right, up and down while walking. Look straight ahead for the gator that will be sitting in the middle of the trail that wasn't there when you went through the first time.
Good luck and enjoy!
My website:
http://dhaass.smugmug.com/Photography/Wildlife
Brazos Bend SP website:
http://www.tpwd.state.tx.us/spdest/f...s/brazos_bend/