There are two possible approaches to the Acropolis, depending on your interests. If you're deep into the classics – or just want to be sure you're not hiking around in the heat – plan to be at the gate at opening time. This gives you about 45 minutes before the tour groups arrive, and you can stay as long as you like.
The other strategy – call it Acropolis Lite – is to go 60 to 90 minutes before closing. At this time, all the big groups have departed, and the sun will be slanting low enough for good photos. Read up before you go, and don't dawdle; go straight to the Parthenon, which is the area the staff start clearing first, then work your way down the southern slopes.
In either case, reserve midday for the air-conditioned confines of the Acropolis Museum, where you can also grab lunch at the super-scenic and relaxing cafe. And allow a little time around sunset to join the volta (stroll) along the pedestrian avenue of Dionysiou Areopagitou and on into Thisio.
For dinner, you can stay close and have dinner with an Acropolis view, or stroll down into Makrygianni and Koukaki for more neighbourhoody options. Shoppers may want to come this way earlier in the day, so as not to miss the little strip of creative boutiques on Veïkou.