If you're planning to go see Elephanta, there are two ways to do it - one is by taking the 2:00 p.m. boat. You'll get to the island at 3:00, when it starts to cool down a bit. There's a twenty minute uphill climb. Fortunately, it is a shady climb with lots of space to sit down and rest, and there are little shops all along the climb where you can browse and shop. Don't forget to take bottled water. You'll have until 4:30 to see the caves, before you need to come downhill. You can take the 5:00 p.m. boat back.
The other way is to take the first boat out at 9:00 a.m. before the crowds come in. That's what I did yesterday.
If you take the 9:00 a.m. boat, you'll be up the hill by ten thirty, and after an hour at the caves, you can come down and take the 12:00 noon boat. The boat ride is actually pretty nice, its cool and breezy in the lower deck.
This is me on the upper deck of the boat. It was sunny but not hot. I paid ten rupees extra for the upper deck (weird, you'd have thought the cool lower decks would be more expensive).
You can see the Gateway of India in the background. The tall building is the new wing of the Taj Mahal Hotel, it completely dwarfs the Gateway from some angles. To the left is the old heritage wing of the Taj Mahal Hotel. They are renovating/repairing the dome.
P.S. Check out my 'sensible' shoes.