I have my first mass start ride this weekend. It's the El Tour de Phoenix, a 72-mile charity ride. I have been training for it a couple of months now and have had my last 3 long rides be 55 miles, 65 miles, and 80 miles, so I think I am prepared. The problem is, I would like to finish it faster than I finished my long rides. Anyway to increase my speed and not die/injure myself, or is it too late to prepare anything?

Too late.

Enjoy the ride.

With all the adrenaline from the excitement, you'll probably just need to make sure you don't over do it for the first few miles! And with a ton of people comes tons of drafting! Eat right, hydrate right, sleep right, maybe a little rolling pin on the legs and you'll kick ass!

will probably depend on a number of factors including wind ,# of riders, traffic lights etc etc. Sounds like you are prepared to cover the distance and I would suggest not being concerned too much about the time. Unless you have timed yourself on this particular route it will be tough to guage anyways. I've found riding in these events it is best to just go with the flow and stay out of trouble as you will see all levels of riders and if you find some open road then go for it.

Just ride your ride and don't stop too long at the rest stops and you'll probably be pleased with your effort.