We spent a day but didn't get there till 11:30 because we were moving hotels and checking in (at Hill City). Had lunch at Sylvan Lake Lodge, walked around the lake a few minutes and then drove the Needles Hwy. with a few stops. Went from there to Wildlife Drive since we were mainly there for the animals. After that we stopped by the main VC but didn't stay long since a tour bus had just disgorged a million people. Then drove 16A back to Mt. Rushmore, arriving there about 8:30; this gave us time for a bowl of mediocre chili but not time to get a seat for the evening lighting program. But this was fine because it wasn't too long to stand and we could see fine. (Probably could have found a seat if we'd wanted to try.)

Custer was something of an afterthought since I hadn't heard of it till hunting something else on this forum, but luckily I had built in an extra day because Custer was our favorite of the SD itinerary. We liked it so much - great animal viewing - that after we went to Wind Cave the next morning, we drove back through Custer on the Wildlife loop and on to Mt. Rush. again on 16A. We had hoped going earlier in the day would give us better views of Rushmore through the tunnels and lookouts on 16A but the atmosphere was a little murky. Nevertheless, that's a nice trip. We got to Rushmore this time about 6PM and had time to walk around the base, see the studio before dark. (Didn't stay for the evening program again, headed back to Hill City for dinner in a restaurant.) This was sufficient for looking around but if you want to take some hikes or do any of the other things in the park, you'd have to cut some of the drives or add time. If we'd had more time, we probably would have gone back for at least half a day. (You can check Days 3 and 4 of my (overly long) trip report from June. ("Sixteen Days in Yellowstone, WY, SD, MT")