Here's a few suggestions if camping at the Acorn site in Llantwit Major.
You can drive there via Junction 33 and Cardiff and swing around the coast, but it's probably faster to leave the M4 at Junction 35, near Bridgend, and follow the A473 until it meets the A48 and then head towards Cowbridge. At Pentre Meyrick take the B4268 to Llantwit Major.
For a dawn shoot at the lowest tide, the Caisson at West Aberthaw would be excellent. It's a short distance back towards Cardiff and there is parking at the beach. For a more leisurely start, there is a rocky beach close to the Acorn site. It doesn't seem to have a proper name but on the Google Maps close up 'The Beach Cafe' is marked. Easy parking.
The lighthouses at Nash Point, (south of Marcross) might be the main meeting point at say, 9.30-10.00. Parts of the beach would still be accessible as the tide comes in, but the highlight (pun alert) would be the lighthouses themselves on their rocky promontory. Incidentally, early morning there is often a neat veil of mist across the channel, with the hilltops of Devon rising above it in the distance.
One could easily spend a couple of hours at Nash Point, and fair coffee is available at the Horseshoe Inn at Marcross, just back up the road. We could even have lunch there as well.
After lunch, we can head to Dunraven Bay. The tide will still be up, but the walled garden of Dunraven Park is worth exploring first, both for the layout of the demolished mansion and for the views across the coast. Lots of parking space, but there is a charge at weekends.
If anyone gets bored waiting for the tide to go out again, a short trip away beyond Ogmore-by-Sea there are the ruins of Ogmore Castle. It's a Cadw site and entry is free. And in late afternoon, Dunraven Bay itself can take up many hours.
Dinner, tbc.
Tides, rocks, and grassy slopes need good footwear.
