Hi Karly, when I did this tour a couple of years ago, we stopped at the Vegas sign as part of the Vegas by night tour - it was quiet then and we had plenty of time to take photos of the sign which actually came out really well.
If you don't book any of the excursions to the Grand Canyon you'll have a free day in Vegas. One of our tour didn't as she had been there before and another in our group booked a bus tour to the GC independently - I wouldn't recommend doing that as she was on a bus for around 12 hours! If you haven't been to the GC I'd really recommend it, an amazing experience. I did the 3-in-1 tour, as did almost everyone on our tour: the coach took us to Boulder City airport and we took a small plane to the south rim; then we got on helicopters to the bottom of the canyon, a short boat trip along the Colorado river, then into the chopper again back up to the top, then a bus tour to visit various viewing points as well as a picnic breakfast. It was an early start - around 4.30am I think, but we were back around 1.30pm for lunch in the Stratosphere. It's expensive but worth it!
Hope this helps,
Bob